Bash Cookbook

Recipes for Bash (Bourne Again shell).

Hands-on Bash examples and guides for daily work.

https://lucas-six.github.io/bash-cookbook/

Installation and Update

Linux

Bash is the default shell for Linux.

Ubuntu, Debian

apt install bash bash-completion

Red Hat (RHEL, CentOS, Fedora)

dnf install -y bash bash-completion

or

yum install -y bash bash-completion

macOS

Homebrew

brew install bash bash-completion@2
chsh -s /usr/local/bin/bash

Builitin

Basic

cd [~|-|..|<dir>]
pwd  # $PWD
ls [-l|-a|-r|-h|-R]
less <file>
ln -s[f] <src> <symlink>
cp|mv [-r|-u] <src ...> <dst>
rm [-r|-f] <file ...>|<dir>
mkdir [-p] [-m <mode>] <dir>
rmdir [-p] <empty-dir>
wc -l <file>
head|tail -n <num> <file>
tail -f <file>
cut -d -f

type

$ type type
type is a shell builtin

$ type cp
cp is /usr/bin/cp

$ type ls
ls is aliased to 'ls --color=auto'

Help

help <builtin-cmd>

<cmd> --help
man|info [section] <cmd>
which [-a] <cmd>

Key Bindings

• Tab - Command Completion
• Ctrl+D - exit or EOF
• Ctrl+C - SIGTERM
• Ctrl+A / Ctrl+E - Go to Beginning / End of Command Line
• Ctrl+U / Ctrl+K - Cut from Current Position to Beginning / End of Command Line
• Ctrl+Left / Ctrl+Right - Go to Previous / Next Word
• Ctrl+Y - Paste
• Ctrl+L - clear
• Ctrl+R - History Search, Ctrl+C to Quit
• Ctrl+Z - SIGSTP
• Ctrl+- - Undo

Output

echo [-n|-e] <str>

Environment Variables

echo $PWD   # current directory
echo $USER  # current user name
echo $HOME  # home directory of current user

Input / Output

Input

From stdin

DEFAULT="default"
read -t 5 -p "Prompt [$DEFAULT]: " VAR
if [[ $? != 0 ]]; then
    echo "xxx"
fi
VAR=${VAR:-$DEFAULT}

From File

cat > /etc/pip.conf <<EOF
[global]
index-url = https://pypi.douban.com/simple

[list]
format = columns
EOF

Output Redirection

Redirect stderr

ls -l /bin/usr 2> ls-error.log

Redirect stdout and stderr

ls -l /bin/usr &> ls.log  # Bash 4.0+
ls -l /bin/usr > ls.log 2>&1

Redirect stdout and stderr

ls -l /bin/usr &> ls.log  # Bash 4.0+
ls -l /bin/usr > ls.log 2>&1

Sometimes “silence is golden”

ls -l /bin/usr > /dev/null 2>ls.log

Expansion

• pathname expansion: *.txt
• tilde expansion: ~
• brace expansion: {a,b}, {A..C}
• command substitution: $(echo a)
• arithmetic expansion: $((1+1))
• parameter expansion: $USER

$ echo text ~/*.txt {a,b} {A..C} $(echo a) $((1+1)) $USER
text /home/ly/a.txt a b A B C a 2 ly

$ echo "text ~/*.txt {a,b} {A..C} $(echo a) $((1+1)) $USER"
text ~/*.txt {a,b} {A..C} a 2 ly

$ echo 'text ~/*.txt {a,b} {A..C} $(echo a) $((1+1)) $USER'
text ~/*.txt {a,b} {A..C} $(echo a) $((1+1)) $USER

Text Processing

Subtitute

str="a-b-c"
echo ${str/-/_}_d   # a_b-c_d
echo ${str//-/_}_d  # a_b_c_d

Substring

str="abcdef"
echo ${str:1}       # a
echo ${str:2:2}     # bc

Testing Operator

-z empty
-n NOT empty

Regular Expression

• * - Any numbers of characters
• ? - Any single character
• [abc] - Any character in set of abc
• [!abc] - Any character NOT in set of abc
• [:alpha:] - Any letter
• [:lower:] - Any lower-case letter
• [:upper:] - Any upper-case letter
• [:digit:] - Any digit
• [:alnum:] - [[:alpha:][:digit:]]
• [:word:] - [[:alnum:]_]*
• [:blank:] - Space + Tab
• ^abc - Any line started with abc
• abc$ - Any line ended with abc
• + - More than once
• {n}, {n,m} - From (n) to (m) times

Startup Files

Login Shell Sessions

• ~/.bash_profile
• ~/.bash_login
• ~/.profile
• /etc/profile
• /etc/profile.d/*.sh

Non-Login Shell Sessions

• ~/.bashrc
• /etc/bash.bashrc

Testing Options

if [[ <-opt> xxx ]]; then
    ...
fi

Used frequently:

-e exist
-s NOT empty
-f regular file
-d directory
-S socket
-p named pipe
-h symbolic link
-r readable
-w writable
-nt newer than
-ot older than
-ef hard link

Loop Over Array

a=(1 2)
for i in ${a[*]}; do
    echo $i
done

References

• The Bash Reference Manual