libbb: introduce and use is_prefixed_with()

function                                             old     new   delta
is_prefixed_with                                       -      18     +18
complete_username                                     78      77      -1
man_main                                             737     735      -2
fsck_device                                          429     427      -2
unpack_ar_archive                                     80      76      -4
strip_unsafe_prefix                                  105     101      -4
singlemount                                         1054    1050      -4
rtc_adjtime_is_utc                                    90      86      -4
resolve_mount_spec                                    88      84      -4
parse_one_line                                      1029    1025      -4
parse_conf                                          1460    1456      -4
may_wakeup                                            83      79      -4
loadkmap_main                                        219     215      -4
get_irqs_from_stat                                   103      99      -4
get_header_cpio                                      913     909      -4
findfs_main                                           79      75      -4
fbsplash_main                                       1230    1226      -4
load_crontab                                         776     771      -5
expand_vars_to_list                                 1151    1146      -5
date_main                                            881     876      -5
skip_dev_pfx                                          30      24      -6
make_device                                         2199    2193      -6
complete_cmd_dir_file                                773     767      -6
run_applet_and_exit                                  715     708      -7
uudecode_main                                        321     313      -8
pwdx_main                                            197     189      -8
execute                                              568     560      -8
i2cdetect_main                                      1186    1176     -10
procps_scan                                         1242    1230     -12
procps_read_smaps                                   1017    1005     -12
process_module                                       746     734     -12
patch_main                                          1903    1891     -12
nfsmount                                            3572    3560     -12
stack_machine                                        126     112     -14
process_timer_stats                                  449     435     -14
match_fstype                                         111      97     -14
do_ipaddr                                           1344    1330     -14
open_list_and_close                                  359     343     -16
get_header_tar                                      1795    1779     -16
prepend_new_eth_table                                340     323     -17
fsck_main                                           1811    1794     -17
find_iface_state                                      56      38     -18
dnsd_main                                           1321    1303     -18
base_device                                          179     158     -21
find_keyword                                         104      82     -22
handle_incoming_and_exit                            2785    2762     -23
parse_and_put_prompt                                 774     746     -28
modinfo                                              347     317     -30
find_action                                          204     171     -33
update_passwd                                       1470    1436     -34
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 0/49 up/down: 18/-540)         Total: -522 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

51 files changed, 165 insertions, 151 deletions

diff --git a/archival/libarchive/get_header_cpio.c b/archival/libarchive/get_header_cpio.c
index 1a0058b63..7861d1f6f 100644
--- a/archival/libarchive/get_header_cpio.c
+++ b/archival/libarchive/get_header_cpio.c
@@ -37,7 +37,7 @@ char FAST_FUNC get_header_cpio(archive_handle_t *archive_handle)
         }
         archive_handle->offset += 110;
 
-        if (strncmp(&cpio_header[0], "07070", 5) != 0
+        if (!is_prefixed_with(&cpio_header[0], "07070")
          || (cpio_header[5] != '1' && cpio_header[5] != '2')
         ) {
                 bb_error_msg_and_die("unsupported cpio format, use newc or crc");
diff --git a/archival/libarchive/get_header_tar.c b/archival/libarchive/get_header_tar.c
index 0c663fbd7..2dbcdb50c 100644
--- a/archival/libarchive/get_header_tar.c
+++ b/archival/libarchive/get_header_tar.c
@@ -105,7 +105,7 @@ static void process_pax_hdr(archive_handle_t *archive_handle, unsigned sz, int g
                 value = end + 1;
 
 #if ENABLE_FEATURE_TAR_GNU_EXTENSIONS
-                if (!global && strncmp(value, "path=", sizeof("path=") - 1) == 0) {
+                if (!global && is_prefixed_with(value, "path=")) {
                         value += sizeof("path=") - 1;
                         free(archive_handle->tar__longname);
                         archive_handle->tar__longname = xstrdup(value);
@@ -118,7 +118,7 @@ static void process_pax_hdr(archive_handle_t *archive_handle, unsigned sz, int g
                  * This is what Red Hat's patched version of tar uses.
                  */
 # define SELINUX_CONTEXT_KEYWORD "RHT.security.selinux"
-                if (strncmp(value, SELINUX_CONTEXT_KEYWORD"=", sizeof(SELINUX_CONTEXT_KEYWORD"=") - 1) == 0) {
+                if (is_prefixed_with(value, SELINUX_CONTEXT_KEYWORD"=")) {
                         value += sizeof(SELINUX_CONTEXT_KEYWORD"=") - 1;
                         free(archive_handle->tar__sctx[global]);
                         archive_handle->tar__sctx[global] = xstrdup(value);
@@ -202,7 +202,7 @@ char FAST_FUNC get_header_tar(archive_handle_t *archive_handle)
 
         /* Check header has valid magic, "ustar" is for the proper tar,
          * five NULs are for the old tar format  */
-        if (strncmp(tar.magic, "ustar", 5) != 0
+        if (!is_prefixed_with(tar.magic, "ustar")
          && (!ENABLE_FEATURE_TAR_OLDGNU_COMPATIBILITY
              || memcmp(tar.magic, "\0\0\0\0", 5) != 0)
         ) {
diff --git a/archival/libarchive/unpack_ar_archive.c b/archival/libarchive/unpack_ar_archive.c
index 214d17e23..0bc030349 100644
--- a/archival/libarchive/unpack_ar_archive.c
+++ b/archival/libarchive/unpack_ar_archive.c
@@ -12,7 +12,7 @@ void FAST_FUNC unpack_ar_archive(archive_handle_t *ar_archive)
         char magic[7];
 
         xread(ar_archive->src_fd, magic, AR_MAGIC_LEN);
-        if (strncmp(magic, AR_MAGIC, AR_MAGIC_LEN) != 0) {
+        if (!is_prefixed_with(magic, AR_MAGIC)) {
                 bb_error_msg_and_die("invalid ar magic");
         }
         ar_archive->offset += AR_MAGIC_LEN;
diff --git a/archival/libarchive/unsafe_prefix.c b/archival/libarchive/unsafe_prefix.c
index 826c673bf..9994f4d94 100644
--- a/archival/libarchive/unsafe_prefix.c
+++ b/archival/libarchive/unsafe_prefix.c
@@ -15,7 +15,7 @@ const char* FAST_FUNC strip_unsafe_prefix(const char *str)
                         cp++;
                         continue;
                 }
-                if (strncmp(cp, "/../"+1, 3) == 0) {
+                if (is_prefixed_with(cp, "/../"+1)) {
                         cp += 3;
                         continue;
                 }
diff --git a/console-tools/loadkmap.c b/console-tools/loadkmap.c
index 6dcf8133f..f525ee5d1 100644
--- a/console-tools/loadkmap.c
+++ b/console-tools/loadkmap.c
@@ -57,7 +57,7 @@ int loadkmap_main(int argc UNUSED_PARAM, char **argv)
 */
 
         xread(STDIN_FILENO, flags, 7);
-        if (strncmp(flags, BINARY_KEYMAP_MAGIC, 7))
+        if (!is_prefixed_with(flags, BINARY_KEYMAP_MAGIC))
                 bb_error_msg_and_die("not a valid binary keymap");
 
         xread(STDIN_FILENO, flags, MAX_NR_KEYMAPS);
diff --git a/coreutils/date.c b/coreutils/date.c
index 767e0d4a2..7965775fe 100644
--- a/coreutils/date.c
+++ b/coreutils/date.c
@@ -373,7 +373,7 @@ int date_main(int argc UNUSED_PARAM, char **argv)
                 date_buf[0] = '\0';
         } else {
                 /* Handle special conversions */
-                if (strncmp(fmt_dt2str, "%f", 2) == 0) {
+                if (is_prefixed_with(fmt_dt2str, "%f")) {
                         fmt_dt2str = (char*)"%Y.%m.%d-%H:%M:%S";
                 }
                 /* Generate output string */
diff --git a/coreutils/uudecode.c b/coreutils/uudecode.c
index b298fcb95..3f1227306 100644
--- a/coreutils/uudecode.c
+++ b/coreutils/uudecode.c
@@ -110,10 +110,10 @@ int uudecode_main(int argc UNUSED_PARAM, char **argv)
                 FILE *dst_stream;
                 int mode;
 
-                if (strncmp(line, "begin-base64 ", 13) == 0) {
+                if (is_prefixed_with(line, "begin-base64 ")) {
                         line_ptr = line + 13;
                         decode_fn_ptr = read_base64;
-                } else if (strncmp(line, "begin ", 6) == 0) {
+                } else if (is_prefixed_with(line, "begin ")) {
                         line_ptr = line + 6;
                         decode_fn_ptr = read_stduu;
                 } else {
diff --git a/e2fsprogs/fsck.c b/e2fsprogs/fsck.c
index d32f396e9..d2d312e5c 100644
--- a/e2fsprogs/fsck.c
+++ b/e2fsprogs/fsck.c
@@ -199,7 +199,7 @@ static char *base_device(const char *device)
         }
 
         /* Handle DAC 960 devices */
-        if (strncmp(cp, "rd/", 3) == 0) {
+        if (is_prefixed_with(cp, "rd/")) {
                 cp += 3;
                 if (cp[0] != 'c' || !isdigit(cp[1])
                  || cp[2] != 'd' || !isdigit(cp[3]))
@@ -224,9 +224,9 @@ static char *base_device(const char *device)
 #if ENABLE_FEATURE_DEVFS
         /* Now let's handle devfs (ugh) names */
         len = 0;
-        if (strncmp(cp, "ide/", 4) == 0)
+        if (is_prefixed_with(cp, "ide/"))
                 len = 4;
-        if (strncmp(cp, "scsi/", 5) == 0)
+        if (is_prefixed_with(cp, "scsi/"))
                 len = 5;
         if (len) {
                 cp += len;
@@ -237,38 +237,38 @@ static char *base_device(const char *device)
                  * some number of digits at each level, abort.
                  */
                 for (hier = devfs_hier; *hier; hier++) {
-                        len = strlen(*hier);
-                        if (strncmp(cp, *hier, len) != 0)
+                        cp = is_prefixed_with(cp, *hier);
+                        if (!cp)
                                 goto errout;
-                        cp += len;
-                        while (*cp != '/' && *cp != 0) {
+                        while (*cp != '/' && *cp != '\0') {
                                 if (!isdigit(*cp))
                                         goto errout;
                                 cp++;
                         }
+//FIXME: what if *cp = '\0' now? cp++ moves past it!!!
                         cp++;
                 }
-                cp[-1] = 0;
+                cp[-1] = '\0';
                 return str;
         }
 
         /* Now handle devfs /dev/disc or /dev/disk names */
-        disk = 0;
-        if (strncmp(cp, "discs/", 6) == 0)
+        disk = NULL;
+        if (is_prefixed_with(cp, "discs/"))
                 disk = "disc";
-        else if (strncmp(cp, "disks/", 6) == 0)
+        else if (is_prefixed_with(cp, "disks/"))
                 disk = "disk";
         if (disk) {
                 cp += 6;
-                if (strncmp(cp, disk, 4) != 0)
+                cp = is_prefixed_with(cp, disk);
+                if (!cp)
                         goto errout;
-                cp += 4;
-                while (*cp != '/' && *cp != 0) {
+                while (*cp != '/' && *cp != '\0') {
                         if (!isdigit(*cp))
                                 goto errout;
                         cp++;
                 }
-                *cp = 0;
+                *cp = '\0';
                 return str;
         }
 #endif
@@ -593,8 +593,8 @@ static void fsck_device(struct fs_info *fs /*, int interactive */)
                                         type, "from fstab");
         } else if (fstype
          && (fstype[0] != 'n' || fstype[1] != 'o') /* != "no" */
-         && strncmp(fstype, "opts=", 5) != 0
-         && strncmp(fstype, "loop", 4) != 0
+         && !is_prefixed_with(fstype, "opts=")
+         && !is_prefixed_with(fstype, "loop")
          && !strchr(fstype, ',')
         ) {
                 type = fstype;
@@ -627,8 +627,8 @@ static int device_already_active(char *device)
 #ifdef BASE_MD
         /* Don't check a soft raid disk with any other disk */
         if (instance_list
-         && (!strncmp(instance_list->device, BASE_MD, sizeof(BASE_MD)-1)
-             || !strncmp(device, BASE_MD, sizeof(BASE_MD)-1))
+         && (is_prefixed_with(instance_list->device, BASE_MD)
+             || is_prefixed_with(device, BASE_MD))
         ) {
                 return 1;
         }
@@ -895,7 +895,7 @@ static void compile_fs_type(char *fs_type)
                 if (strcmp(s, "loop") == 0)
                         /* loop is really short-hand for opts=loop */
                         goto loop_special_case;
-                if (strncmp(s, "opts=", 5) == 0) {
+                if (is_prefixed_with(s, "opts=")) {
                         s += 5;
  loop_special_case:
                         fs_type_flag[num] = negate ? FS_TYPE_FLAG_NEGOPT : FS_TYPE_FLAG_OPT;
diff --git a/editors/patch.c b/editors/patch.c
index f86067544..cb25e4140 100644
--- a/editors/patch.c
+++ b/editors/patch.c
@@ -414,7 +414,7 @@ int patch_main(int argc UNUSED_PARAM, char **argv)
                 }
 
                 // Open a new file?
-                if (!strncmp("--- ", patchline, 4) || !strncmp("+++ ", patchline, 4)) {
+                if (is_prefixed_with(patchline, "--- ") || is_prefixed_with(patchline, "+++ ")) {
                         char *s, **name = reverse ? &newname : &oldname;
                         int i;
 
@@ -446,7 +446,7 @@ int patch_main(int argc UNUSED_PARAM, char **argv)
 
                 // Start a new hunk?  Usually @@ -oldline,oldlen +newline,newlen @@
                 // but a missing ,value means the value is 1.
-                } else if (state == 1 && !strncmp("@@ -", patchline, 4)) {
+                } else if (state == 1 && is_prefixed_with(patchline, "@@ -")) {
                         int i;
                         char *s = patchline+4;
 
diff --git a/include/libbb.h b/include/libbb.h
index be792d6b2..c97df6047 100644
--- a/include/libbb.h
+++ b/include/libbb.h
@@ -389,6 +389,7 @@ const char *bb_basename(const char *name) FAST_FUNC;
 /* NB: can violate const-ness (similarly to strchr) */
 char *last_char_is(const char *s, int c) FAST_FUNC;
 const char* endofname(const char *name) FAST_FUNC;
+char *is_prefixed_with(const char *string, const char *key) FAST_FUNC;
 
 int ndelay_on(int fd) FAST_FUNC;
 int ndelay_off(int fd) FAST_FUNC;
diff --git a/libbb/appletlib.c b/libbb/appletlib.c
index 54300bd87..8fd8fd525 100644
--- a/libbb/appletlib.c
+++ b/libbb/appletlib.c
@@ -193,7 +193,7 @@ void lbb_prepare(const char *applet
         if (argv[1]
          && !argv[2]
          && strcmp(argv[1], "--help") == 0
-         && strncmp(applet, "busybox", 7) != 0
+         && !is_prefixed_with(applet, "busybox")
         ) {
                 /* Special case. POSIX says "test --help"
                  * should be no different from e.g. "test --foo".  */
@@ -673,7 +673,7 @@ static int busybox_main(char **argv)
                 return 0;
         }
 
-        if (strncmp(argv[1], "--list", 6) == 0) {
+        if (is_prefixed_with(argv[1], "--list")) {
                 unsigned i = 0;
                 const char *a = applet_names;
                 dup2(1, 2);
@@ -778,7 +778,7 @@ void FAST_FUNC run_applet_and_exit(const char *name, char **argv)
         int applet = find_applet_by_name(name);
         if (applet >= 0)
                 run_applet_no_and_exit(applet, argv);
-        if (strncmp(name, "busybox", 7) == 0)
+        if (is_prefixed_with(name, "busybox"))
                 exit(busybox_main(argv));
 }
 
@@ -817,7 +817,7 @@ int main(int argc UNUSED_PARAM, char **argv)
 
 #if defined(SINGLE_APPLET_MAIN)
         /* Only one applet is selected in .config */
-        if (argv[1] && strncmp(argv[0], "busybox", 7) == 0) {
+        if (argv[1] && is_prefixed_with(argv[0], "busybox")) {
                 /* "busybox <applet> <params>" should still work as expected */
                 argv++;
         }
diff --git a/libbb/compare_string_array.c b/libbb/compare_string_array.c
index 4b10cc138..e24815a03 100644
--- a/libbb/compare_string_array.c
+++ b/libbb/compare_string_array.c
@@ -5,6 +5,24 @@
 
 #include "libbb.h"
 
+char* FAST_FUNC is_prefixed_with(const char *string, const char *key)
+{
+#if 0   /* Two passes over key - probably slower */
+        int len = strlen(key);
+        if (strncmp(string, key, len) == 0)
+                return string + len;
+        return NULL;
+#else   /* Open-coded */
+        while (*key != '\0') {
+                if (*key != *string)
+                        return NULL;
+                key++;
+                string++;
+        }
+        return (char*)string;
+#endif
+}
+
 /* returns the array index of the string */
 /* (index of first match is returned, or -1) */
 int FAST_FUNC index_in_str_array(const char *const string_array[], const char *key)
@@ -39,10 +57,9 @@ int FAST_FUNC index_in_strings(const char *strings, const char *key)
 int FAST_FUNC index_in_substr_array(const char *const string_array[], const char *key)
 {
         int i;
-        int len = strlen(key);
-        if (len) {
+        if (key[0]) {
                 for (i = 0; string_array[i] != 0; i++) {
-                        if (strncmp(string_array[i], key, len) == 0) {
+                        if (is_prefixed_with(string_array[i], key)) {
                                 return i;
                         }
                 }
diff --git a/libbb/lineedit.c b/libbb/lineedit.c
index 249b401b4..a83e07c0c 100644
--- a/libbb/lineedit.c
+++ b/libbb/lineedit.c
@@ -681,7 +681,7 @@ static NOINLINE unsigned complete_username(const char *ud)
         setpwent();
         while ((pw = getpwent()) != NULL) {
                 /* Null usernames should result in all users as possible completions. */
-                if (/*!userlen || */ strncmp(ud, pw->pw_name, userlen) == 0) {
+                if (/* !ud[0] || */ is_prefixed_with(pw->pw_name, ud)) {
                         add_match(xasprintf("~%s/", pw->pw_name));
                 }
         }
@@ -792,7 +792,7 @@ static NOINLINE unsigned complete_cmd_dir_file(const char *command, int type)
                         if (!pfind[0] && DOT_OR_DOTDOT(name_found))
                                 continue;
                         /* match? */
-                        if (strncmp(name_found, pfind, pf_len) != 0)
+                        if (!is_prefixed_with(name_found, pfind))
                                 continue; /* no */
 
                         found = concat_path_file(paths[i], name_found);
@@ -1879,15 +1879,16 @@ static void parse_and_put_prompt(const char *prmt_ptr)
                                                 cwd_buf = xrealloc_getcwd_or_warn(NULL);
                                                 if (!cwd_buf)
                                                         cwd_buf = (char *)bb_msg_unknown;
-                                                else {
+                                                else if (home_pwd_buf[0]) {
+                                                        char *after_home_user;
+
                                                         /* /home/user[/something] -> ~[/something] */
-                                                        l = strlen(home_pwd_buf);
-                                                        if (l != 0
-                                                         && strncmp(home_pwd_buf, cwd_buf, l) == 0
-                                                         && (cwd_buf[l] == '/' || cwd_buf[l] == '\0')
+                                                        after_home_user = is_prefixed_with(cwd_buf, home_pwd_buf);
+                                                        if (after_home_user
+                                                         && (*after_home_user == '/' || *after_home_user == '\0')
                                                         ) {
                                                                 cwd_buf[0] = '~';
-                                                                overlapping_strcpy(cwd_buf + 1, cwd_buf + l);
+                                                                overlapping_strcpy(cwd_buf + 1, after_home_user);
                                                         }
                                                 }
                                         }
diff --git a/libbb/match_fstype.c b/libbb/match_fstype.c
index 32c3d7f18..b066b4211 100644
--- a/libbb/match_fstype.c
+++ b/libbb/match_fstype.c
@@ -17,7 +17,6 @@
 int FAST_FUNC match_fstype(const struct mntent *mt, const char *t_fstype)
 {
         int match = 1;
-        int len;
 
         if (!t_fstype)
                 return match;
@@ -27,10 +26,10 @@ int FAST_FUNC match_fstype(const struct mntent *mt, const char *t_fstype)
                 t_fstype += 2;
         }
 
-        len = strlen(mt->mnt_type);
         while (1) {
-                if (strncmp(mt->mnt_type, t_fstype, len) == 0
-                 && (t_fstype[len] == '\0' || t_fstype[len] == ',')
+                char *after_mnt_type = is_prefixed_with(t_fstype, mt->mnt_type);
+                if (after_mnt_type
+                 && (*after_mnt_type == '\0' || *after_mnt_type == ',')
                 ) {
                         return match;
                 }
diff --git a/libbb/procps.c b/libbb/procps.c
index 5b68d3431..948b91ee6 100644
--- a/libbb/procps.c
+++ b/libbb/procps.c
@@ -205,11 +205,11 @@ int FAST_FUNC procps_read_smaps(pid_t pid, struct smaprec *total,
                 // Rss:                 nnn kB
                 // .....
 
-                char *tp = buf, *p;
+                char *tp, *p;
 
 #define SCAN(S, X) \
-                if (strncmp(tp, S, sizeof(S)-1) == 0) {              \
-                        tp = skip_whitespace(tp + sizeof(S)-1);      \
+                if ((tp = is_prefixed_with(buf, S)) != NULL) {       \
+                        tp = skip_whitespace(tp);                    \
                         total->X += currec.X = fast_strtoul_10(&tp); \
                         continue;                                    \
                 }
@@ -247,7 +247,7 @@ int FAST_FUNC procps_read_smaps(pid_t pid, struct smaprec *total,
                         // skipping "rw-s FILEOFS M:m INODE "
                         tp = skip_whitespace(skip_fields(tp, 4));
                         // filter out /dev/something (something != zero)
-                        if (strncmp(tp, "/dev/", 5) != 0 || strcmp(tp, "/dev/zero\n") == 0) {
+                        if (!is_prefixed_with(tp, "/dev/") || strcmp(tp, "/dev/zero\n") == 0) {
                                 if (currec.smap_mode[1] == 'w') {
                                         currec.mapped_rw = currec.smap_size;
                                         total->mapped_rw += currec.smap_size;
@@ -497,8 +497,8 @@ procps_status_t* FAST_FUNC procps_scan(procps_status_t* sp, int flags)
                                 while (fgets(buf, sizeof(buf), file)) {
                                         char *tp;
 #define SCAN_TWO(str, name, statement) \
-        if (strncmp(buf, str, sizeof(str)-1) == 0) { \
-                tp = skip_whitespace(buf + sizeof(str)-1); \
+        if ((tp = is_prefixed_with(buf, str)) != NULL) { \
+                tp = skip_whitespace(tp); \
                 sscanf(tp, "%u", &sp->name); \
                 statement; \
         }
diff --git a/libbb/rtc.c b/libbb/rtc.c
index 6d06d57f9..c4117ba34 100644
--- a/libbb/rtc.c
+++ b/libbb/rtc.c
@@ -22,7 +22,7 @@ int FAST_FUNC rtc_adjtime_is_utc(void)
                 char buffer[128];
 
                 while (fgets(buffer, sizeof(buffer), f)) {
-                        if (strncmp(buffer, "UTC", 3) == 0) {
+                        if (is_prefixed_with(buffer, "UTC")) {
                                 utc = 1;
                                 break;
                         }
diff --git a/libbb/skip_whitespace.c b/libbb/skip_whitespace.c
index 8c7b674c3..b6cfbba4d 100644
--- a/libbb/skip_whitespace.c
+++ b/libbb/skip_whitespace.c
@@ -33,7 +33,7 @@ char* FAST_FUNC skip_non_whitespace(const char *s)
 
 char* FAST_FUNC skip_dev_pfx(const char *tty_name)
 {
-        if (strncmp(tty_name, "/dev/", 5) == 0)
+        if (is_prefixed_with(tty_name, "/dev/"))
                 tty_name += 5;
         return (char*)tty_name;
 }
diff --git a/libbb/update_passwd.c b/libbb/update_passwd.c
index dc26ebd1d..a2004f480 100644
--- a/libbb/update_passwd.c
+++ b/libbb/update_passwd.c
@@ -84,7 +84,6 @@ int FAST_FUNC update_passwd(const char *filename,
         char *fnamesfx;
         char *sfx_char;
         char *name_colon;
-        unsigned user_len;
         int old_fd;
         int new_fd;
         int i;
@@ -108,7 +107,6 @@ int FAST_FUNC update_passwd(const char *filename,
         fnamesfx = xasprintf("%s+", filename);
         sfx_char = &fnamesfx[strlen(fnamesfx)-1];
         name_colon = xasprintf("%s:", name ? name : "");
-        user_len = strlen(name_colon);
 
         if (shadow)
                 old_fp = fopen(filename, "r+");
@@ -179,7 +177,7 @@ int FAST_FUNC update_passwd(const char *filename,
                         while (list) {
                                 list++;
  next_list_element:
-                                if (strncmp(list, member, member_len) == 0) {
+                                if (is_prefixed_with(list, member)) {
                                         char c;
                                         changed_lines++;
                                         c = list[member_len];
@@ -201,13 +199,14 @@ int FAST_FUNC update_passwd(const char *filename,
                         goto next;
                 }
 
-                if (strncmp(name_colon, line, user_len) != 0) {
+                cp = is_prefixed_with(line, name_colon);
+                if (!cp) {
                         fprintf(new_fp, "%s\n", line);
                         goto next;
                 }
 
                 /* We have a match with "name:"... */
-                cp = line + user_len; /* move past name: */
+                /* cp points past "name:" */
 
 #if ENABLE_FEATURE_ADDUSER_TO_GROUP || ENABLE_FEATURE_DEL_USER_FROM_GROUP
                 if (member) {
diff --git a/libbb/xconnect.c b/libbb/xconnect.c
index 1c8bb2b73..2a96e03dc 100644
--- a/libbb/xconnect.c
+++ b/libbb/xconnect.c
@@ -171,7 +171,7 @@ IF_NOT_FEATURE_IPV6(sa_family_t af = AF_INET;)
         const char *cp;
         struct addrinfo hint;
 
-        if (ENABLE_FEATURE_UNIX_LOCAL && strncmp(host, "local:", 6) == 0) {
+        if (ENABLE_FEATURE_UNIX_LOCAL && is_prefixed_with(host, "local:")) {
                 struct sockaddr_un *sun;
 
                 r = xzalloc(LSA_LEN_SIZE + sizeof(struct sockaddr_un));
diff --git a/miscutils/crond.c b/miscutils/crond.c
index 3659b9a6f..eb327f855 100644
--- a/miscutils/crond.c
+++ b/miscutils/crond.c
@@ -438,14 +438,14 @@ static void load_crontab(const char *fileName)
                         log5("user:%s entry:%s", fileName, parser->data);
 
                         /* check if line is setting MAILTO= */
-                        if (0 == strncmp(tokens[0], "MAILTO=", 7)) {
+                        if (is_prefixed_with(tokens[0], "MAILTO=")) {
 #if ENABLE_FEATURE_CROND_CALL_SENDMAIL
                                 free(mailTo);
                                 mailTo = (tokens[0][7]) ? xstrdup(&tokens[0][7]) : NULL;
 #endif /* otherwise just ignore such lines */
                                 continue;
                         }
-                        if (0 == strncmp(tokens[0], "SHELL=", 6)) {
+                        if (is_prefixed_with(tokens[0], "SHELL=")) {
                                 free(shell);
                                 shell = xstrdup(&tokens[0][6]);
                                 continue;
diff --git a/miscutils/dc.c b/miscutils/dc.c
index a7bd360d2..f94d6fa6b 100644
--- a/miscutils/dc.c
+++ b/miscutils/dc.c
@@ -244,9 +244,9 @@ static void stack_machine(const char *argument)
 
         o = operators;
         do {
-                const size_t name_len = strlen(o->name);
-                if (strncmp(o->name, argument, name_len) == 0) {
-                        argument += name_len;
+                char *after_name = is_prefixed_with(argument, o->name);
+                if (after_name) {
+                        argument = after_name;
                         o->function();
                         goto next;
                 }
diff --git a/miscutils/devfsd.c b/miscutils/devfsd.c
index 96ffe0738..5a6aec6bd 100644
--- a/miscutils/devfsd.c
+++ b/miscutils/devfsd.c
@@ -1405,7 +1405,6 @@ const char *get_old_name(const char *devname, unsigned int namelen,
         int indexx;
         const char *pty1;
         const char *pty2;
-        size_t len;
         /* 1 to 5  "scsi/" , 6 to 9 "ide/host", 10 sbp/, 11 vcc/, 12 pty/ */
         static const char *const fmt[] = {
                 NULL ,
@@ -1425,12 +1424,11 @@ const char *get_old_name(const char *devname, unsigned int namelen,
         };
 
         for (trans = translate_table; trans->match != NULL; ++trans) {
-                len = strlen(trans->match);
-
-                if (strncmp(devname, trans->match, len) == 0) {
+                char *after_match = is_prefixed_with(devname, trans->match);
+                if (after_match) {
                         if (trans->format == NULL)
-                                return devname + len;
-                        sprintf(buffer, trans->format, devname + len);
+                                return after_match;
+                        sprintf(buffer, trans->format, after_match);
                         return buffer;
                 }
         }
diff --git a/miscutils/fbsplash.c b/miscutils/fbsplash.c
index 7b695b26f..77033c258 100644
--- a/miscutils/fbsplash.c
+++ b/miscutils/fbsplash.c
@@ -516,7 +516,7 @@ int fbsplash_main(int argc UNUSED_PARAM, char **argv)
         // handle a case when we have many buffered lines
         // already in the pipe
         while ((num_buf = xmalloc_fgetline(fp)) != NULL) {
-                if (strncmp(num_buf, "exit", 4) == 0) {
+                if (is_prefixed_with(num_buf, "exit")) {
                         DEBUG_MESSAGE("exit");
                         break;
                 }
diff --git a/miscutils/i2c_tools.c b/miscutils/i2c_tools.c
index 90d1e1e14..03bb03974 100644
--- a/miscutils/i2c_tools.c
+++ b/miscutils/i2c_tools.c
@@ -1198,7 +1198,7 @@ static void NORETURN list_i2c_busses_and_exit(void)
                                 if (subde->d_name[0] == '.')
                                         continue;
 
-                                if (strncmp(subde->d_name, "i2c-", 4) == 0) {
+                                if (is_prefixed_with(subde->d_name, "i2c-")) {
                                         snprintf(path, NAME_MAX,
                                                  "%s/%s/device/%s/name",
                                                  i2cdev_path, de->d_name,
@@ -1229,7 +1229,7 @@ found:
                         if (rv != 1)
                                 continue;
 
-                        if (strncmp(name, "ISA", 3) == 0)
+                        if (is_prefixed_with(name, "ISA"))
                                 adt = ADT_ISA;
                         else
                                 adt = i2cdetect_get_funcs(bus);
diff --git a/miscutils/last.c b/miscutils/last.c
index 24f6e1c78..a144c7e47 100644
--- a/miscutils/last.c
+++ b/miscutils/last.c
@@ -87,11 +87,11 @@ int last_main(int argc UNUSED_PARAM, char **argv UNUSED_PARAM)
                         if (++n > 0)
                                 ut.ut_type = n != 3 ? n : SHUTDOWN_TIME;
 #else
-                        if (strncmp(ut.ut_user, "shutdown", 8) == 0)
+                        if (is_prefixed_with(ut.ut_user, "shutdown"))
                                 ut.ut_type = SHUTDOWN_TIME;
-                        else if (strncmp(ut.ut_user, "reboot", 6) == 0)
+                        else if (is_prefixed_with(ut.ut_user, "reboot"))
                                 ut.ut_type = BOOT_TIME;
-                        else if (strncmp(ut.ut_user, "runlevel", 8) == 0)
+                        else if (is_prefixed_with(ut.ut_user, "runlevel"))
                                 ut.ut_type = RUN_LVL;
 #endif
                 } else {
diff --git a/miscutils/man.c b/miscutils/man.c
index c39870e67..58ed81955 100644
--- a/miscutils/man.c
+++ b/miscutils/man.c
@@ -66,7 +66,7 @@ static int run_pipe(const char *pager, char *man_filename, int man, int level)
                         goto ordinary_manpage;
 
                 line = xmalloc_open_zipped_read_close(man_filename, NULL);
-                if (!line || strncmp(line, ".so ", 4) != 0) {
+                if (!line || !is_prefixed_with(line, ".so ")) {
                         free(line);
                         goto ordinary_manpage;
                 }
@@ -228,7 +228,7 @@ int man_main(int argc UNUSED_PARAM, char **argv)
                 if (!token[1])
                         continue;
                 if (strcmp("DEFINE", token[0]) == 0) {
-                        if (strncmp("pager", token[1], 5) == 0) {
+                        if (is_prefixed_with("pager", token[1])) {
                                 pager = xstrdup(skip_whitespace(token[1]) + 5);
                         }
                 } else
diff --git a/modutils/depmod.c b/modutils/depmod.c
index 37a8482d9..9713aef92 100644
--- a/modutils/depmod.c
+++ b/modutils/depmod.c
@@ -55,7 +55,7 @@ static int FAST_FUNC parse_module(const char *fname, struct stat *sb UNUSED_PARA
                         NULL
         );
         for (ptr = image; ptr < image + len - 10; ptr++) {
-                if (strncmp(ptr, "depends=", 8) == 0) {
+                if (is_prefixed_with(ptr, "depends=")) {
                         char *u;
 
                         ptr += 8;
@@ -64,15 +64,15 @@ static int FAST_FUNC parse_module(const char *fname, struct stat *sb UNUSED_PARA
                                         *u = '_';
                         ptr += string_to_llist(ptr, &info->dependencies, ",");
                 } else if (ENABLE_FEATURE_MODUTILS_ALIAS
-                 && strncmp(ptr, "alias=", 6) == 0
+                 && is_prefixed_with(ptr, "alias=")
                 ) {
                         llist_add_to(&info->aliases, xstrdup(ptr + 6));
                         ptr += strlen(ptr);
                 } else if (ENABLE_FEATURE_MODUTILS_SYMBOLS
-                 && strncmp(ptr, "__ksymtab_", 10) == 0
+                 && is_prefixed_with(ptr, "__ksymtab_")
                 ) {
                         ptr += 10;
-                        if (strncmp(ptr, "gpl", 3) == 0
+                        if (is_prefixed_with(ptr, "gpl")
                          || strcmp(ptr, "strings") == 0
                         ) {
                                 continue;
diff --git a/modutils/modinfo.c b/modutils/modinfo.c
index ee379304c..8e74b6438 100644
--- a/modutils/modinfo.c
+++ b/modutils/modinfo.c
@@ -62,7 +62,7 @@ static void modinfo(const char *path, const char *version,
                 "firmware",
         };
         size_t len;
-        int j, length;
+        int j;
         char *ptr, *the_module;
         const char *field = env->field;
         int tags = env->tags;
@@ -94,16 +94,18 @@ static void modinfo(const char *path, const char *version,
                 pattern = field;
                 if ((1<<j) & OPT_TAGS)
                         pattern = shortcuts[j];
-                length = strlen(pattern);
                 ptr = the_module;
                 while (1) {
+                        char *after_pattern;
+
                         ptr = memchr(ptr, *pattern, len - (ptr - (char*)the_module));
                         if (ptr == NULL) /* no occurance left, done */
                                 break;
-                        if (strncmp(ptr, pattern, length) == 0 && ptr[length] == '=') {
+                        after_pattern = is_prefixed_with(ptr, pattern);
+                        if (after_pattern && *after_pattern == '=') {
                                 /* field prefixes are 0x80 or 0x00 */
-                                if ((ptr[-1] & 0x7F) == '\0') {
-                                        ptr += length + 1;
+                                if ((ptr[-1] & 0x7F) == 0x00) {
+                                        ptr = after_pattern + 1;
                                         display(ptr, pattern, (1<<j) != tags);
                                         ptr += strlen(ptr);
                                 }
diff --git a/modutils/modprobe-small.c b/modutils/modprobe-small.c
index ed177bb9b..9c941064b 100644
--- a/modutils/modprobe-small.c
+++ b/modutils/modprobe-small.c
@@ -116,21 +116,21 @@ static char* copy_stringbuf(void)
 
 static char* find_keyword(char *ptr, size_t len, const char *word)
 {
-        int wlen;
-
         if (!ptr) /* happens if xmalloc_open_zipped_read_close cannot read it */
                 return NULL;
 
-        wlen = strlen(word);
-        len -= wlen - 1;
+        len -= strlen(word) - 1;
         while ((ssize_t)len > 0) {
                 char *old = ptr;
+                char *after_word;
+
                 /* search for the first char in word */
-                ptr = memchr(ptr, *word, len);
+                ptr = memchr(ptr, word[0], len);
                 if (ptr == NULL) /* no occurance left, done */
                         break;
-                if (strncmp(ptr, word, wlen) == 0)
-                        return ptr + wlen; /* found, return ptr past it */
+                after_word = is_prefixed_with(ptr, word);
+                if (after_word)
+                        return after_word; /* found, return ptr past it */
                 ++ptr;
                 len -= (ptr - old);
         }
@@ -536,7 +536,7 @@ static module_info** find_alias(const char *alias)
 // TODO: open only once, invent config_rewind()
 static int already_loaded(const char *name)
 {
-        int ret, namelen;
+        int ret;
         char *line;
         FILE *fp;
 
@@ -545,15 +545,16 @@ static int already_loaded(const char *name)
         fp = fopen_for_read("/proc/modules");
         if (!fp)
                 return 0;
-        namelen = strlen(name);
         while ((line = xmalloc_fgetline(fp)) != NULL) {
                 char *live;
+                char *after_name;
 
                 // Examples from kernel 3.14.6:
                 //pcspkr 12718 0 - Live 0xffffffffa017e000
                 //snd_timer 28690 2 snd_seq,snd_pcm, Live 0xffffffffa025e000
                 //i915 801405 2 - Live 0xffffffffa0096000
-                if (strncmp(line, name, namelen) != 0 || line[namelen] != ' ') {
+                after_name = is_prefixed_with(line, name);
+                if (!after_name || *after_name != ' ') {
                         free(line);
                         continue;
                 }
diff --git a/modutils/modprobe.c b/modutils/modprobe.c
index 0e8aa9e85..996de4074 100644
--- a/modutils/modprobe.c
+++ b/modutils/modprobe.c
@@ -260,7 +260,7 @@ static void add_probe(const char *name)
         llist_add_to_end(&G.probes, m);
         G.num_unresolved_deps++;
         if (ENABLE_FEATURE_MODUTILS_SYMBOLS
-         && strncmp(m->modname, "symbol:", 7) == 0
+         && is_prefixed_with(m->modname, "symbol:")
         ) {
                 G.need_symbols = 1;
         }
@@ -353,22 +353,18 @@ static char *parse_and_add_kcmdline_module_options(char *options, const char *mo
         char *kcmdline_buf;
         char *kcmdline;
         char *kptr;
-        int len;
 
         kcmdline_buf = xmalloc_open_read_close("/proc/cmdline", NULL);
         if (!kcmdline_buf)
                 return options;
 
         kcmdline = kcmdline_buf;
-        len = strlen(modulename);
         while ((kptr = strsep(&kcmdline, "\n\t ")) != NULL) {
-                if (strncmp(modulename, kptr, len) != 0)
-                        continue;
-                kptr += len;
-                if (*kptr != '.')
+                char *after_modulename = is_prefixed_with(kptr, modulename);
+                if (!after_modulename || *after_modulename != '.')
                         continue;
                 /* It is "modulename.xxxx" */
-                kptr++;
+                kptr = after_modulename + 1;
                 if (strchr(kptr, '=') != NULL) {
                         /* It is "modulename.opt=[val]" */
                         options = gather_options_str(options, kptr);
diff --git a/modutils/modutils-24.c b/modutils/modutils-24.c
index 12cb75c54..fe46fc3fd 100644
--- a/modutils/modutils-24.c
+++ b/modutils/modutils-24.c
@@ -2255,7 +2255,7 @@ static int add_symbols_from(struct obj_file *f,
                  * symbols so they cannot fudge it by adding the prefix on
                  * their references.
                  */
-                if (strncmp((char *)s->name, "GPLONLY_", 8) == 0) {
+                if (is_prefixed_with((char *)s->name, "GPLONLY_")) {
 #if ENABLE_FEATURE_CHECK_TAINTED_MODULE
                         if (gpl)
                                 s->name += 8;
diff --git a/networking/dnsd.c b/networking/dnsd.c
index fe98400f7..923ad6bc6 100644
--- a/networking/dnsd.c
+++ b/networking/dnsd.c
@@ -194,7 +194,7 @@ static char *table_lookup(struct dns_entry *d,
                 if ((len != 1 || d->name[1] != '*')
                 /* we assume (do not check) that query_string
                  * ends in ".in-addr.arpa" */
-                 && strncmp(d->rip, query_string, strlen(d->rip)) == 0
+                 && is_prefixed_with(query_string, d->rip)
                 ) {
 #if DEBUG
                         fprintf(stderr, "Found name:%s\n", d->name);
diff --git a/networking/httpd.c b/networking/httpd.c
index 9cf080401..7a9065fcc 100644
--- a/networking/httpd.c
+++ b/networking/httpd.c
@@ -697,7 +697,7 @@ static void parse_conf(const char *path, int flag)
                                 goto config_error;
                         }
                         *host_port++ = '\0';
-                        if (strncmp(host_port, "http://", 7) == 0)
+                        if (is_prefixed_with(host_port, "http://"))
                                 host_port += 7;
                         if (*host_port == '\0') {
                                 goto config_error;
@@ -1894,7 +1894,7 @@ static Htaccess_Proxy *find_proxy_entry(const char *url)
 {
         Htaccess_Proxy *p;
         for (p = proxy; p; p = p->next) {
-                if (strncmp(url, p->url_from, strlen(p->url_from)) == 0)
+                if (is_prefixed_with(url, p->url_from))
                         return p;
         }
         return NULL;
@@ -2183,7 +2183,7 @@ static void handle_incoming_and_exit(const len_and_sockaddr *fromAddr)
                         if (STRNCASECMP(iobuf, "Range:") == 0) {
                                 /* We know only bytes=NNN-[MMM] */
                                 char *s = skip_whitespace(iobuf + sizeof("Range:")-1);
-                                if (strncmp(s, "bytes=", 6) == 0) {
+                                if (is_prefixed_with(s, "bytes=") == 0) {
                                         s += sizeof("bytes=")-1;
                                         range_start = BB_STRTOOFF(s, &s, 10);
                                         if (s[0] != '-' || range_start < 0) {
@@ -2269,7 +2269,7 @@ static void handle_incoming_and_exit(const len_and_sockaddr *fromAddr)
         tptr = urlcopy + 1;      /* skip first '/' */
 
 #if ENABLE_FEATURE_HTTPD_CGI
-        if (strncmp(tptr, "cgi-bin/", 8) == 0) {
+        if (is_prefixed_with(tptr, "cgi-bin/")) {
                 if (tptr[8] == '\0') {
                         /* protect listing "cgi-bin/" */
                         send_headers_and_exit(HTTP_FORBIDDEN);
diff --git a/networking/ifupdown.c b/networking/ifupdown.c
index c35d97a1a..daabeec0c 100644
--- a/networking/ifupdown.c
+++ b/networking/ifupdown.c
@@ -289,7 +289,7 @@ static char *parse(const char *command, struct interface_defn_t *ifd)
                                         /* "hwaddress <class> <address>":
                                          * unlike ifconfig, ip doesnt want <class>
                                          * (usually "ether" keyword). Skip it. */
-                                        if (strncmp(command, "hwaddress", 9) == 0) {
+                                        if (is_prefixed_with(command, "hwaddress")) {
                                                 varvalue = skip_whitespace(skip_non_whitespace(varvalue));
                                         }
 # endif
@@ -298,7 +298,7 @@ static char *parse(const char *command, struct interface_defn_t *ifd)
 # if ENABLE_FEATURE_IFUPDOWN_IP
                                         /* Sigh...  Add a special case for 'ip' to convert from
                                          * dotted quad to bit count style netmasks.  */
-                                        if (strncmp(command, "bnmask", 6) == 0) {
+                                        if (is_prefixed_with(command, "bnmask")) {
                                                 unsigned res;
                                                 varvalue = get_var("netmask", 7, ifd);
                                                 if (varvalue) {
@@ -1159,12 +1159,12 @@ static char *run_mapping(char *physical, struct mapping_defn_t *map)
 
 static llist_t *find_iface_state(llist_t *state_list, const char *iface)
 {
-        unsigned iface_len = strlen(iface);
         llist_t *search = state_list;
 
         while (search) {
-                if ((strncmp(search->data, iface, iface_len) == 0)
-                 && (search->data[iface_len] == '=')
+                char *after_iface = is_prefixed_with(search->data, iface);
+                if (after_iface
+                 && *after_iface == '='
                 ) {
                         return search;
                 }
diff --git a/networking/inetd.c b/networking/inetd.c
index 8148925ce..dce5a0885 100644
--- a/networking/inetd.c
+++ b/networking/inetd.c
@@ -727,7 +727,7 @@ static NOINLINE servtab_t *parse_one_line(void)
                         goto parse_err;
 #endif
                 }
-                if (strncmp(arg, "rpc/", 4) == 0) {
+                if (is_prefixed_with(arg, "rpc/")) {
 #if ENABLE_FEATURE_INETD_RPC
                         unsigned n;
                         arg += 4;
diff --git a/networking/libiproute/ipaddress.c b/networking/libiproute/ipaddress.c
index aa4779ad1..4072d0626 100644
--- a/networking/libiproute/ipaddress.c
+++ b/networking/libiproute/ipaddress.c
@@ -701,7 +701,7 @@ static int ipaddr_modify(int cmd, char **argv)
                 /* There was no "dev IFACE", but we need that */
                 bb_error_msg_and_die("need \"dev IFACE\"");
         }
-        if (l && strncmp(d, l, strlen(d)) != 0) {
+        if (l && !is_prefixed_with(l, d)) {
                 bb_error_msg_and_die("\"dev\" (%s) must match \"label\" (%s)", d, l);
         }
 
diff --git a/networking/nameif.c b/networking/nameif.c
index 9a8846dc0..9b18a6d16 100644
--- a/networking/nameif.c
+++ b/networking/nameif.c
@@ -161,19 +161,19 @@ static void nameif_parse_selector(ethtable_t *ch, char *selector)
                 if (*next)
                         *next++ = '\0';
                 /* Check for selectors, mac= is assumed */
-                if (strncmp(selector, "bus=", 4) == 0) {
+                if (is_prefixed_with(selector, "bus=")) {
                         ch->bus_info = xstrdup(selector + 4);
                         found_selector++;
-                } else if (strncmp(selector, "driver=", 7) == 0) {
+                } else if (is_prefixed_with(selector, "driver=")) {
                         ch->driver = xstrdup(selector + 7);
                         found_selector++;
-                } else if (strncmp(selector, "phyaddr=", 8) == 0) {
+                } else if (is_prefixed_with(selector, "phyaddr=")) {
                         ch->phy_address = xatoi_positive(selector + 8);
                         found_selector++;
                 } else {
 #endif
                         lmac = xmalloc(ETH_ALEN);
-                        ch->mac = ether_aton_r(selector + (strncmp(selector, "mac=", 4) != 0 ? 0 : 4), lmac);
+                        ch->mac = ether_aton_r(selector + (is_prefixed_with(selector, "mac=") ? 4 : 0), lmac);
                         if (ch->mac == NULL)
                                 bb_error_msg_and_die("can't parse %s", selector);
 #if  ENABLE_FEATURE_NAMEIF_EXTENDED
diff --git a/networking/netstat.c b/networking/netstat.c
index f80b845bc..02f4cc7cc 100644
--- a/networking/netstat.c
+++ b/networking/netstat.c
@@ -228,12 +228,12 @@ static long extract_socket_inode(const char *lname)
 {
         long inode = -1;
 
-        if (strncmp(lname, "socket:[", sizeof("socket:[")-1) == 0) {
+        if (is_prefixed_with(lname, "socket:[")) {
                 /* "socket:[12345]", extract the "12345" as inode */
                 inode = bb_strtoul(lname + sizeof("socket:[")-1, (char**)&lname, 0);
                 if (*lname != ']')
                         inode = -1;
-        } else if (strncmp(lname, "[0000]:", sizeof("[0000]:")-1) == 0) {
+        } else if (is_prefixed_with(lname, "[0000]:")) {
                 /* "[0000]:12345", extract the "12345" as inode */
                 inode = bb_strtoul(lname + sizeof("[0000]:")-1, NULL, 0);
                 if (errno) /* not NUL terminated? */
diff --git a/procps/mpstat.c b/procps/mpstat.c
index af3263d67..6028903fa 100644
--- a/procps/mpstat.c
+++ b/procps/mpstat.c
@@ -526,7 +526,7 @@ static void get_irqs_from_stat(struct stats_irq *irq)
 
         while (fgets(buf, sizeof(buf), fp)) {
                 //bb_error_msg("/proc/stat:'%s'", buf);
-                if (strncmp(buf, "intr ", 5) == 0) {
+                if (is_prefixed_with(buf, "intr ")) {
                         /* Read total number of IRQs since system boot */
                         sscanf(buf + 5, "%"FMT_DATA"u", &irq->irq_nr);
                 }
diff --git a/procps/powertop.c b/procps/powertop.c
index ddda5bd93..18affacdd 100644
--- a/procps/powertop.c
+++ b/procps/powertop.c
@@ -458,9 +458,9 @@ static NOINLINE int process_timer_stats(void)
                         //      func = "Load balancing tick";
                         //}
 
-                        if (strncmp(func, "tick_nohz_", 10) == 0)
+                        if (is_prefixed_with(func, "tick_nohz_"))
                                 continue;
-                        if (strncmp(func, "tick_setup_sched_timer", 20) == 0)
+                        if (is_prefixed_with(func, "tick_setup_sched_timer"))
                                 continue;
                         //if (strcmp(process, "powertop") == 0)
                         //      continue;
diff --git a/procps/pwdx.c b/procps/pwdx.c
index 22b892275..4e34149ed 100644
--- a/procps/pwdx.c
+++ b/procps/pwdx.c
@@ -41,7 +41,7 @@ int pwdx_main(int argc UNUSED_PARAM, char **argv)
                 // Allowed on the command line:
                 // /proc/NUM
                 // NUM
-                if (strncmp(arg, "/proc/", 6) == 0)
+                if (is_prefixed_with(arg, "/proc/"))
                         arg += 6;
 
                 pid = bb_strtou(arg, NULL, 10);
diff --git a/shell/hush.c b/shell/hush.c
index 92d790180..f2c0a70f2 100644
--- a/shell/hush.c
+++ b/shell/hush.c
@@ -5884,7 +5884,7 @@ static FILE *generate_stream_from_string(const char *s, pid_t *pid_p)
                  * Our solution: ONLY bare $(trap) or `trap` is special.
                  */
                 s = skip_whitespace(s);
-                if (strncmp(s, "trap", 4) == 0
+                if (is_prefixed_with(s, "trap")
                  && skip_whitespace(s + 4)[0] == '\0'
                 ) {
                         static const char *const argv[] = { NULL, NULL };
diff --git a/util-linux/acpid.c b/util-linux/acpid.c
index fc8151f6a..0f2cb6bdc 100644
--- a/util-linux/acpid.c
+++ b/util-linux/acpid.c
@@ -151,7 +151,7 @@ static const char *find_action(struct input_event *ev, const char *buf)
                 }
 
                 if (buf) {
-                        if (strncmp(buf, evt_tab[i].desc, strlen(buf)) == 0) {
+                        if (is_prefixed_with(evt_tab[i].desc, buf)) {
                                 action = evt_tab[i].desc;
                                 break;
                         }
diff --git a/util-linux/fdisk.c b/util-linux/fdisk.c
index 39eb27b47..7fe70fb72 100644
--- a/util-linux/fdisk.c
+++ b/util-linux/fdisk.c
@@ -2781,14 +2781,14 @@ is_ide_cdrom_or_tape(const char *device)
            the process hangs on the attempt to read a music CD.
            So try to be careful. This only works since 2.1.73. */
 
-        if (strncmp("/dev/hd", device, 7))
+        if (!is_prefixed_with(device, "/dev/hd"))
                 return 0;
 
         snprintf(buf, sizeof(buf), "/proc/ide/%s/media", device+5);
         procf = fopen_for_read(buf);
         if (procf != NULL && fgets(buf, sizeof(buf), procf))
-                is_ide = (!strncmp(buf, "cdrom", 5) ||
-                          !strncmp(buf, "tape", 4));
+                is_ide = (is_prefixed_with(buf, "cdrom") ||
+                          is_prefixed_with(buf, "tape"));
         else
                 /* Now when this proc file does not exist, skip the
                    device when it is read-only. */
diff --git a/util-linux/fdisk_osf.c b/util-linux/fdisk_osf.c
index ff16389bd..af04cfcc8 100644
--- a/util-linux/fdisk_osf.c
+++ b/util-linux/fdisk_osf.c
@@ -854,7 +854,7 @@ xbsd_initlabel(struct partition *p)
 
         d->d_magic = BSD_DISKMAGIC;
 
-        if (strncmp(disk_device, "/dev/sd", 7) == 0)
+        if (is_prefixed_with(disk_device, "/dev/sd"))
                 d->d_type = BSD_DTYPE_SCSI;
         else
                 d->d_type = BSD_DTYPE_ST506;
diff --git a/util-linux/fdisk_sgi.c b/util-linux/fdisk_sgi.c
index 785fc661b..23ebc56ef 100644
--- a/util-linux/fdisk_sgi.c
+++ b/util-linux/fdisk_sgi.c
@@ -440,7 +440,7 @@ sgi_write_table(void)
                 (unsigned int*)sgilabel, sizeof(*sgilabel)) == 0);
 
         write_sector(0, sgilabel);
-        if (!strncmp((char*)sgilabel->directory[0].vol_file_name, "sgilabel", 8)) {
+        if (is_prefixed_with((char*)sgilabel->directory[0].vol_file_name, "sgilabel")) {
                 /*
                  * keep this habit of first writing the "sgilabel".
                  * I never tested whether it works without (AN 981002).
diff --git a/util-linux/findfs.c b/util-linux/findfs.c
index 49e8979ac..07734f359 100644
--- a/util-linux/findfs.c
+++ b/util-linux/findfs.c
@@ -27,7 +27,7 @@ int findfs_main(int argc UNUSED_PARAM, char **argv)
         if (!dev)
                 bb_show_usage();
 
-        if (strncmp(dev, "/dev/", 5) == 0) {
+        if (is_prefixed_with(dev, "/dev/")) {
                 /* Just pass any /dev/xxx name right through.
                  * This might aid in some scripts being able
                  * to call this unconditionally */
diff --git a/util-linux/mdev.c b/util-linux/mdev.c
index b2d56575f..ccc00d365 100644
--- a/util-linux/mdev.c
+++ b/util-linux/mdev.c
@@ -610,7 +610,7 @@ static void make_device(char *device_name, char *path, int operation)
          * We use strstr("/block/") to forestall future surprises.
          */
         type = S_IFCHR;
-        if (strstr(path, "/block/") || (G.subsystem && strncmp(G.subsystem, "block", 5) == 0))
+        if (strstr(path, "/block/") || (G.subsystem && is_prefixed_with(G.subsystem, "block")))
                 type = S_IFBLK;
 
 #if ENABLE_FEATURE_MDEV_CONF
diff --git a/util-linux/mount.c b/util-linux/mount.c
index fbc89c862..cb40c802d 100644
--- a/util-linux/mount.c
+++ b/util-linux/mount.c
@@ -641,7 +641,7 @@ static llist_t *get_block_backed_filesystems(void)
                 if (!f) continue;
 
                 while ((buf = xmalloc_fgetline(f)) != NULL) {
-                        if (strncmp(buf, "nodev", 5) == 0 && isspace(buf[5]))
+                        if (is_prefixed_with(buf, "nodev") && isspace(buf[5]))
                                 goto next;
                         fs = skip_whitespace(buf);
                         if (*fs == '#' || *fs == '*' || !*fs)
@@ -1364,9 +1364,9 @@ static NOINLINE int nfsmount(struct mntent *mp, unsigned long vfsflags, char *fi
                                                 strcspn(opteq, " \t\n\r,"));
                                 continue;
                         case 18: // "proto"
-                                if (!strncmp(opteq, "tcp", 3))
+                                if (is_prefixed_with(opteq, "tcp"))
                                         tcp = 1;
-                                else if (!strncmp(opteq, "udp", 3))
+                                else if (is_prefixed_with(opteq, "udp"))
                                         tcp = 0;
                                 else
                                         bb_error_msg("warning: unrecognized proto= option");
@@ -1459,7 +1459,7 @@ static NOINLINE int nfsmount(struct mntent *mp, unsigned long vfsflags, char *fi
                                 "rdirplus\0"
                                 "acl\0";
                         int val = 1;
-                        if (!strncmp(opt, "no", 2)) {
+                        if (is_prefixed_with(opt, "no")) {
                                 val = 0;
                                 opt += 2;
                         }
@@ -1979,7 +1979,7 @@ static int singlemount(struct mntent *mp, int ignore_busy)
         }
 
         // Might this be an NFS filesystem?
-        if ((!mp->mnt_type || strncmp(mp->mnt_type, "nfs", 3) == 0)
+        if ((!mp->mnt_type || is_prefixed_with(mp->mnt_type, "nfs"))
          && strchr(mp->mnt_fsname, ':') != NULL
         ) {
                 if (!mp->mnt_type)
diff --git a/util-linux/rtcwake.c b/util-linux/rtcwake.c
index 53d9384db..8aee0cfcb 100644
--- a/util-linux/rtcwake.c
+++ b/util-linux/rtcwake.c
@@ -66,7 +66,7 @@ static NOINLINE bool may_wakeup(const char *rtcname)
                 return false;
 
         /* wakeup events could be disabled or not supported */
-        return strncmp(buf, "enabled\n", 8) == 0;
+        return is_prefixed_with(buf, "enabled\n") != NULL;
 }
 
 static NOINLINE void setup_alarm(int fd, time_t *wakeup, time_t rtc_time)
diff --git a/util-linux/volume_id/get_devname.c b/util-linux/volume_id/get_devname.c
index 0c6bdfddf..53bdbdf09 100644
--- a/util-linux/volume_id/get_devname.c
+++ b/util-linux/volume_id/get_devname.c
@@ -302,9 +302,9 @@ int resolve_mount_spec(char **fsname)
 {
         char *tmp = *fsname;
 
-        if (strncmp(*fsname, "UUID=", 5) == 0)
+        if (is_prefixed_with(*fsname, "UUID="))
                 tmp = get_devname_from_uuid(*fsname + 5);
-        else if (strncmp(*fsname, "LABEL=", 6) == 0)
+        else if (is_prefixed_with(*fsname, "LABEL=") == 0)
                 tmp = get_devname_from_label(*fsname + 6);
 
         if (tmp == *fsname)