And or list
1
| echo "I am going to do sth" && doSomething 2>/dev/null || error cmd (echo $?)`
|
print the exit code: echo $?
blackhole for information: /dev/null
File redirection
1
2
3
| redirect to file: `> file`
append to file: `>> file`
read from file: `< file`
|
File descriptor
file descriptors:
1
2
3
| 0 - input data
1 - standard out
2 - standard error
|
- throw stdout(file descriptor 1) to file:
command > file
- throw stderr(file descriptor 2) to file:
command 2 > file
- throw both to file:
command > file 2>&1
Utility classes
1
2
3
4
5
6
7
8
| sort
uniq
grep
fmt
tr
head/tail
sed
awk
|
pipe:
Arrays
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
| numbers=(1 2 3 four "5", 6)
$ echo $numbers
1 2 3 four 5, 6
$ echo ${numbers[3]}
3
$ echo ${numbers[@]}
1 2 3 four 5, 6
$ echo ${#numbers[@]}
6
$ numbers+=(seven)
$ echo ${#numbers[@]}
7
$ echo ${numbers[@]}
1 2 3 four 5, 6 seven
$ echo ${numbers[@]:2:4}
3 four 5, 6
$ echo ${numbers[@]:2:2}
3 four
$ echo ${numbers[@]:2}
3 four 5, 6 seven
|
Substitution
1
2
3
4
5
6
| $ cat <(echo "Hello world")
Hello world
$ echo <(echo "Hello world")
/dev/fd/11
$ diff <(ll /folder1) <(ll /folder2)
# output diff files
|
Loop
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
| for i in $(seq 1 10); do
echo "count to $i";
done;
count to 1
...
count to 10
// test command
$ test 10 -lt 0 && echo "false" || echo "true"
true
$ [ 10 -lt 0 ] && echo "false" || echo "true"
true
while [ $Counter -gt 0 ]; do
echo "count to $Counter"
let Counter-=1
done;
count to 10
...
count to 1
until [ $Counter -lt 1 ]; do
echo "count to $Counter"
let Counter-=1
done;
count to 10
...
count to 1
|
Signal/traps
1
2
3
4
5
6
7
8
9
10
11
12
| cleanup()
{
echo "cleaning up ..."
}
trap cleanup SIGINT
while true
do
echo Sleeping
sleep 10
done
|
Heredoc/herestring
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
| $ cat << DELIMITER
heredoc> hello
heredoc> ${USER}
heredoc> DELIMITER
hello
ttingtao
$ cat << "DELIMITER"
heredoc> hello
heredoc> ${USER}
heredoc> DELIMITER
hello
${USER}
$ cat <<- "DELIMITER"
heredocd> hello
heredocd> ${USER}
heredocd> DELIMITER
hello
${USER}
$ VAR="this is a simple test"
$ cat <(echo $VAR)
this is a simple test
$ cat <<< $VAR
this is a simple test
|
Debug scripts
1
2
3
4
5
6
7
8
9
| // dryrun to check syntax error
set -n
// treat unset parameters/variables as error
set -u
// display the expanded command that run
set -x
// add on shebang
#!/bin/bash -x
|
Regex
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
| $ grep -oE "\<of\>" <(echo "of off offff")
of
cat testSedInput
hello word:
------
name: sed
city: vancouver
weather: snowing
------
name: awk
city: singapore
weather: raining
------
$ sed -r '1s/(.+):/Report: \1\n/' testSedInput
Report: hello word
------
name: sed
city: vancouver
weather: snowing
------
name: awk
city: singapore
weather: raining
------
$ sed -r '/-{3,}/d' testSedInput
hello word:
name: sed
city: vancouver
weather: snowing
name: awk
city: singapore
weather: raining
$ sed -r 's/([a-z]+): ([a-z]+)/\1->\2/' testSedInput
hello word:
------
name->sed
city->vancouver
weather->snowing
------
name->awk
city->singapore
weather->raining
------
// or put all sed command into a script
$ cat sedpro.sh
#! /usr/bin/sed
1s/(.+):/Report: \1\n/
/-{3,}/d
s/([a-z]+): ([a-z]+)/\1->\2/
$ sed -E -f sedpro.sh testSedInput
Report->hello word
name->sed
city->vancouver
weather->snowing
name->awk
city->singapore
weather->raining
|
