Bash notes

Turn off bash history for a session

set +o history

Variable Expansion and Substitution

Bash can do some freaky things with variables. It can do lots of other substitutions. See "Parameter Expansion" in the Bash man page.

• ${foo#pattern} - deletes the shortest possible match from the left
• ${foo##pattern} - deletes the longest possible match from the left
• ${foo%pattern} - deletes the shortest possible match from the right
• ${foo%%pattern} - deletes the longest possible match from the right
• ${foo=text} - If $foo exists and is not null then return $foo. If $foo doesn't exist then create it and set value to text.

Statements

Loop on filenames in a directory

for foo in *; do {
  echo ${foo}
}; done

Loop on lines in a file

for foo in $(cat data_file.txt); do {
  echo ${foo}
}; done