• Potohar College of Science Kalar Syedan, Rawalpindi

• ENGR 1340 

Bash command

1. pwd: present working directory

2. man x: manual of command x\

3. mkdir: create directory

a. mkdir lab

b. mkdir lab1 lab2

c. mkdir “lab 1”

4. rmdir: remove directory

5. mv: rename directory

Useful command:

1. rm -rf or rm -r -f: delete entirely a

non-empty directory

2. mv lab “lab1” : rename lab dir to lab1 dir

3. ls -l: list the contents in long format which

contain (file size, owner, …)

4. ls -a: list all contents including hidden

ones.

File management:

1. touch file.txt: create file.txt

2. cat file.txt: display content of file

3. mv hello.txt mydir: move file to dir

Useful commands:

1. cp file1 file2: copy file1 into file2

2. cp -r dir1 dir2: copy dir1 into dir2 incl

sub-dir

3. For mv, if two args are the same type, it act

as a rename func

File Permission:

1.User, group, Other

2.Read(r), write(w), execute(x)

-rw

(-): file

(d): directory

Change permissions:

1.chmod [who][operator][permissions] filename

who: u,g,o,a

Operator: +(add), -(take away permission), = (set

permission)

Other useful command

grep ‘abc’ file

cut -d, -f2 file

wc file (no. lines, words, characters)

sort file (alphabetically)

uniq file (remove adjacent duplicate)

Pipe (|)

find [path] [-name] [-type]

Regular expression

grep -E

. : match any single char

^ : match the beginning

$: match the end

?: zero or one occurrence

+: one or more occurrence

* : zero or more occurrence

[ ]: char inside the bracket will be matched

\: escape char

pattern {n}: match n occurrences of pattern

pattern {n,}: match at least n occurrences

pattern {n,m}: match between n and m occurrences

(ab) {3}: 3 occurrence of ‘ab’

( ) : mark substring

Shell Script

#!/bin/bash

Variable: pet=”dog”

*no space is allowed

To retrieve value, use “$”

Command substitution use backquotes (``)

Get the length of string: ${#a}

Substring: ${a:pos:len}

Replace: ${a/$from/$to}

Mathematical variabile: use “let” code

Get command line arg:

./1.sh hello world

$# = 2

$0 ./1.sh, $1 hello, $2 world

If-else:

if [ condition ]

then

Perform some action

fi

String comparison:

\>: string1 sorted after string2

\<: string1 sorted before string2

File/Directory checking:

[ -e $file ]: true iff file exist

[ -f $file ]: true iff file is file

[ -d $file ]: true iff file is dir

[ -s $file ]: true iff file has size > 0

Number comparison:

[ $a -eq $b ] true iff a = b

[ $a -ne $b ] true iff a != b

[ $a -lt $b ] true iff a < b

[ $a -le $b ] true iff a <= b

[ $a -gt $b ] true iff a > b

[ $a -ge $b ] true iff a >= b

list = “1 2 3 4 5”