Keyboard shortcuts

• C-x C-e — edit command in $EDITOR (vim for me)
• C-a — go to start of command
• C-e — go to end of command
• Alt-f — go forward by word
• Alt-b — go backward by word

Directory stack

• pushd $dir — push cwd to stack, cd to dir
• popd — pop the directory from the stack and cd to it
• dirs — list directory stack

exec builtin

usage:

• with a command: completely replaces shell by program. e.g. exec vim replaces the shell with vim, when you close vim you quit the terminal.
• with a redirection: makes the redirection apply to the current shell

examples:

exec 1> >(lolcat >&2)   # make shell redirect stdout to process lolcat,
                        # which redirects to stderr

exec 3< input.txt        # create a new file descriptor, reading from input.txt
read LINE <&3            # read from the file descriptor into LINE
exec 3<&-                # close the file descriptor

exec 4> output.log       # create a new file descriptor for writing to output.log
echo “foo” >&4           # write “foo” to file descriptor 4 (output.log)
exec 4>&-                # close the file descriptor
echo “foo bar” > file    # write “foo bar” to file
exec 5<>file             # open file for rw on file descriptor 5
read -n 3 var <&5        # read 3 characters from file descriptor 5 into var
echo "Hello" >&5         # write "Hello" into the file
exec 5>&-                # close the file for writing
exec 5<&-                # close the file for reading

Change keybindings

• set -o vi — vim keybindings for shell
• set -o emacs — emacs keybindings for shell

Misc sets

• set -e — exit script on error
• set -x — print code as it executes

Variable expansion

• ${var##*/} — remove longest string of anything followed by / from var
• ${var#*/} — same but shortest
• ${var%%*/} — same as above but from end

Reusing previously typed stuff

• !! — previous command
• !$ — last argument of previous command
• !^ — first argument of previous command
• !* — all arguments of previous command
• !:a-b — arguments number a to b of previous command
• !$:h — only the head of the previous argument (e.g. “/Documents” in “/Documents/file.txt”)
• ^x^y^ — replace x by y in previous command

Redirection

• &> file — redirect all output to a file
• (1)>&2 — redirect stdout to stderr, the 1 is implicit
• 2>&1 — redirect stderr to stdout
• >file — redirect stdout to file, overwriting
• >>file — redirect stdout to file, appending
• <(command) — pass output of command as stdin
• >(command) — redirect stdout to command
• <<< — here string, pass string from stdin as input
• <<EOF ... EOF - here document, pass multiline string as input

order matters, creating a new redirection essentially duplicates the file descriptor (e.g. “command > file 2>&1” != “command 2>&1 > file“

ffmpeg

• ffmpeg -i in.mkv -f srt -i in.srt -map 0:0 -map 0:1 -map 1:0 -c:v copy -c:a copy -c:s srt out.mkv - add subtitles to video
• for f in ./*.ext; do echo "file '$f'" >> list.txt; done; ffmpeg -f concat -safe 0 -i list.txt -c copy output.ext - concatenate videos
• ffmpeg -i in.vtt out.srt - convert vtt subtitles to srt

bc

• bc <<< "obase=2; ibase=16; F" - convert hex to binary (when you set ibase, everything has to be in that base. so if you wanted to reset output to decimal, you’d have to set obase=A).