Misc

Re-exec a shell on the fly

E.g., to apply new shell dotfiles config on-the-fly:

$ exec -l $SHELL

-l: place a - at the beginning of the 1st argument passed Used for a login shell:

A login shell is one whose first character of argument zero is a -, or one started with the --login option.

Turn any command into a file (descriptor)

Use <(cmd):

$ vi <(ls -ls /)

$ diff -Naur <(ls -ls /) <(ls -ls /mnt)

XDG* variables

TL;DR: variables sets when the user logs in! So don't use them in non-login scripts (e.g. cron jobs) with out a fallback: ${XDG_RUNTIME_DIR:-/tmp}

XDG_RUNTIME_DIR

It is an environment variable that is set automatically when you log in.

It tells any program you run where to find a user-specific directory in which it can store small temporary files.

Note that XDG_RUNTIME_DIR is set by pam_systemd(8), so it is not actually related to X (running programs graphically), which is the problem you seem to be having.

Setting a script arguments with set set

Use set -- list of args

$ set -- foo bar fax
$ echo $@
foo bar fax

read

The default read separator is \n, i.e. read until a newline.

• Read all lines in a file with:

$ while read -r line; do COMMAND; done < input.file

• Read until end of file by setting an empty delimer. Also pass -r to read \ as a normal char, with no escape meaning.

read -r -d '' my_variable

• Read from heredoc:

read -r -d '' my_variable << EOF

this is
\ some doc
with quotes ' " ' ' '
 "
EOF

cat as a shell built-in

function cat {
  # if there's only one arg, not starting with a `-`
  if [ $# -eq 1 -a "${1:0:1}" != "-" ]
  then
    # open the input file with fd=3
    exec 3< "${1:-/dev/stdin}"
    while read -r -u3 line
    do
      echo -E ''"${line}";
    done
    echo -nE ''"${line}";
    exec 3<&-
  else
     /bin/cat "$@"
  fi
}

wait

The -n option tells bash to only wait for one PID or jobspec from the provided arguments - whatever terminates first.

E.g.:

# Will only wait for the first PID that terminates among {1,2,3,4}.
$ wait -n 1 2 3 4

# Will wait for all PIDs
$ wait 1 2 3 4

# Will wait for all spawned children
$ wait

Completion for alias command

Allow an alias to use completion of the unaliased command:

alias k=kubectl
complete -F __start_kubectl k