apky/c-utils repository overview

⁠C utils

This is a set of unix utility program that I wrote because I found them helpful.

⁠aenv

Similar to env, but extended to a swiss army knife, to avoid shell processes or shim shells altogether. Options:

• -C arg changes into the given directory.
• -v shows the currently remaining arguments.
• -wN sleeps for N seconds.
• NAME=value sets the environment variable NAME like env does.
• -S NAME values sets the environment variable NAME to value.
• -U NAME unsets the environment variable NAME.
• -I file redirects stdin to read from the given file.
• -O file redirects stdout to write to the given file.
• -X replaces every sequence X<hex><hex> in all following arguments given by the character value <hex><hex>. This is a hack for some ssh versions that s/=/ / on ProxyCommand.
• -Xc similar, but use the given char instead of X.
• --pwnam user change (primary) group and user id to that of the given user. (Requires sufficient privileges.)
• --su user: Like --pwnam, but also sets HOME, USER, and LOGNAME accordingly.
• --id user, --id user:group: change (group and) user id to the given numeric values.
• --fork goes into background by forking and exiting in the foreground process.
• --reaper-fork continues option and argument processing in a forked process. The main process waits for the subprocess to terminate, and also waits for other children, and passes SIGINT and SIGTERM on to the subprocess (and only to that pid). Useful as a docker root process in case of zombies. Each process thus reaped is logged on stderr, with its pid, its exit code if nonzero, and the killing signal if applicable. On linux > 3.4 this works as any process.
• -AN sets alarm() in N seconds, thereby providing a hard timeout for the command finally being executed (caveats apply).
• # arg arg arg (first argument only): hashbang mode. If the first argument begins with a # its second character is taken as a separator, the argument is split at all further occurrences of that character, and that list replaces the first argument as multiple arguments. E.g. the hashbang line #!/usr/bin/aenv #,VAR=value,/usr/bin/ruby will execute the containing script as a ruby script with the environment variable VAR set to value.

Options are processed in order they are given.

The first thing that is not one of the above is taken as the command to execute, with the following arguments as parameters, except if that begins with a minus sign.

If there is no command in the arguments $SHELL or, as a fallback, /bin/sh is started.

⁠cdx

Like aenv, except that the first argument that would otherwise be taken as the command names a directory to change to, and processing continues to the next such argument. So cdx dir git ... is the same as git -C dir ..., and cdx dir GIT_COMMITTER_NAME='John Doe' git ... will pass that environment variable to git.

It's somewhat stupid that the builtin cd or various shells doesn't do this.

⁠rdlog

Like tail -f, except it always outputs the entire file, and it does also follow rename and recreation of the file.

⁠args

Shows its arguments, printing them C-escaped when characters in the values are sufficiently strange. Takes a single option argument as its first argument if that starts with a minus. If a q is there all output is quoted, not only when needed. A m enables multiline output - there will be a newline after each argument instead of everything being on one line. A h causes the option argument itself to be omitted.

⁠xd

Dump each file given as argument as a hex and ascii dump, in the style of early debuggers and monitors. Read stdin if no arguments are given.

⁠escat

Like cat, but escape special characters, and backticks, by a backtick and the two hex digits representing the character. Special characters are everything but printable asccii characters, newlines, tabs, and carriage returns.

With -d it instead decodes backtick escapes bach to the original characters. Backticks not followed by two hex digits are left as they are.