10 Hidden Bash Tricks Every Linux User Should Master

Introduction

I wrote a follow‑up article because the previous one was unexpectedly popular, and I want to share some lesser‑known Bash features that are useful for everyday scripting.

1) History substitution ^x^y^

A quick way to fix a mistyped command by navigating the command history and replacing parts of the previous command.

$ grp somestring somefile
-bash: grp: command not found
$ ^rp^rep^
grep 'somestring' somefile
$

Note the subtle detail when using this technique with other patterns.

2) pushd / popd

Using the directory stack is handy in scripts, especially inside loops. The example shows how to store the original working directory, iterate over sub‑directories, and push/pop directories.

for d1 in $(ls -d */)
do
  original_wd="$(pwd)"
  cd "$d1"
  for d2 in $(ls -d */)
  do
    pushd "$d2"
    # Do something
    popd
  done
  cd "$original_wd"
done

An alternative version rewrites the same logic using only pushd/popd without manual cd.

3) shopt vs set

The shopt builtin lists shell options, while set controls shell behavior. Example output of shopt shows several options and their current state.

$ shopt
cdable_vars    off
cdspell        on
checkhash      off
checkwinsize   on
cmdhist        on
compat31       off
dotglob         off

4) Here Docs and Here Strings

Here Docs let you create a temporary file from inline text until a delimiter word appears on a line by itself.

$ cat > afile << SOMEENDSTRING
here is a doc
it has three lines
SOMEENDSTRING
$ cat afile
here is a doc
it has three lines
SOMEENDSTRING

Here Strings provide a similar mechanism for a single line of input.

$ cat > asd <<< 'This file has one line'

5) String manipulation with parameter expansion

Instead of using sed or awk, Bash can trim prefixes and suffixes directly.

VAR='HEADERMy voice is my passwordFOOTER'
PASS="${VAR#HEADER}"   # removes leading HEADER
PASS="${PASS%FOOTER}"   # removes trailing FOOTER

echo $PASS   # outputs: My voice is my password

The symbols # and % match from the start and end of the string respectively; ## and %% use greedy matching.

6) Variable default values

Use ${var:-default} to supply a fallback when a variable is unset, or ${var:=default} to assign the default value.

#!/bin/bash
FIRST_ARG="${1:-no_first_arg}"
SECOND_ARG="${2:-no_second_arg}"
THIRD_ARG="${3:-no_third_arg}"

echo $FIRST_ARG

echo $SECOND_ARG

echo $THIRD_ARG

7) Traps

Define a cleanup function and register it with trap to run on termination signals.

function cleanup() {
  rm -rf "$BUILD_DIR"
  rm -f "$LOCK_FILE"
  find "$BUILD_DIR_BASE"/* -type d -atime +1 | rm -rf
  echo "cleanup done"
}
trap cleanup TERM INT QUIT

8) Useful shell variables

Examples of built‑in variables:

RANDOM : generates a random integer.

REPLY : holds input when read is used without a variable name.

LINENO and SECONDS : useful for debugging and timing.

TMOUT : sets a timeout for read.

9) Extglobs

Enable extended globbing with shopt -s extglob and use patterns such as +(pattern), *(pattern), ?(pattern), @(pattern), and !(pattern) for advanced matching.

shopt -s extglob
A="12345678901234567890"
B="  $A  "

echo "B      |${B}|"
echo "B#+( ) |${B#+( )}|"
echo "B#?( ) |${B#?( )}|"
echo "B#*( ) |${B#*( )}|"
echo "B##+( )|${B##+( )}|"
echo "B##*( )|${B##*( )}|"
echo "B##?( )|${B##?( )}|"

10) Associative arrays

Available in Bash 4.x+, associative arrays allow string keys.

declare -A MYAA=([one]=1 [two]=2 [three]=3)
MYAA[one]="1"
MYAA[two]="2"

echo ${MYAA[one]}   # prints 1
WANT=two
echo ${MYAA[$WANT]}   # prints 2

Original English article: https://zwischenzugs.com/2018/01/21/ten-more-things-i-wish-id-known-about-bash/ (translated by D)