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Bash: my cookbook
라벨:
Informatics
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TOC
- split a string into charaters
- read a given line
- sort by tab and numeric
- table merge
- array index
- loop
- cheat keys
# split a string into chraters
cat [file] | grep -o .
cat [file] | fold -w1 # seems not working with unicode
# Read a given line
sed -n '90,101p' [file]
# Sort by tab and numeric
sort -t$'\t' --key 8,8 --key 3,3n --key 12,12 --key 9.9 --key 1,1
# Table merge
paste -d , date1.csv date2.csv
# Array Index
${arr[*]} # All of the items in the array
${!arr[*]} # All of the indexes in the array
${#arr[*]} # Number of items in the array
${#arr[0]} # Length of item zero
http://www.linuxjournal.com/content/bash-arrays
# Loop
http://www.cyberciti.biz/faq/bash-for-loop/
Examples
This
type of for loop is characterized by counting. The range is specified
by a beginning (#1) and ending number (#5). The for loop executes a
sequence of commands for each member in a list of items. A
representative example in BASH is as follows to display welcome message 5
times with for loop:
#!/bin/bash
for i in 1 2 3 4 5
do
echo "Welcome $i times"
done
Sometimes you may need to set a step value (allowing one to count by two's or to count backwards for instance). Latest bash version 3.0+ has inbuilt support for setting up ranges:
#!/bin/bash
for i in {1..5}
do
echo "Welcome $i times"
done
Bash v4.0+ has inbuilt support for setting up a step value using {START..END..INCREMENT} syntax:
#!/bin/bash
echo "Bash version ${BASH_VERSION}..."
for i in {0..10..2}
do
echo "Welcome $i times"
done
Sample outputs:
Bash version 4.0.33(0)-release...
Welcome 0 times
Welcome 2 times
Welcome 4 times
Welcome 6 times
Welcome 8 times
Welcome 10 times
The seq command (outdated)
WARNING!
The seq command print a sequence of numbers and it is here due to
historical reasons. The following examples is only recommend for older
bash version. All users (bash v3.x+) are recommended to use the above
syntax.
The seq command can be used as follows. A representative example in seq is as follows:
#!/bin/bash
for i in $(seq 1 2 20)
do
echo "Welcome $i times"
done
There
is no good reason to use an external command such as seq to count and
increment numbers in the for loop, hence it is recommend that you avoid
using seq. The builtin command are fast.
Three-expression bash for loops syntax
This
type of for loop share a common heritage with the C programming
language. It is characterized by a three-parameter loop control
expression; consisting of an initializer (EXP1), a loop-test or
condition (EXP2), and a counting expression (EXP3).
for (( EXP1; EXP2; EXP3 ))
do
command1
command2
command3
done
A representative three-expression example in bash as follows:
#!/bin/bash
for (( c=1; c<=5; c++ ))
do
echo "Welcome $c times"
done
Sample output:
Welcome 1 times
Welcome 2 times
Welcome 3 times
Welcome 4 times
Welcome 5 times
How do I use for as infinite loops?
Infinite for loop can be created with empty expressions, such as:
#!/bin/bash
for (( ; ; ))
do
echo "infinite loops [ hit CTRL+C to stop]"
done
Conditional exit with break
You
can do early exit with break statement inside the for loop. You can
exit from within a FOR, WHILE or UNTIL loop using break. General break
statement inside the for loop:
for I in 1 2 3 4 5
do
statements1 #Executed for all values of ''I'', up to a disaster-condition if any.
statements2
if (disaster-condition)
then
break #Abandon the loop.
fi
statements3 #While good and, no disaster-condition.
done
Following
shell script will go though all files stored in /etc directory. The for
loop will be abandon when /etc/resolv.conf file found.
#!/bin/bash
for file in /etc/*
do
if [ "${file}" == "/etc/resolv.conf" ]
then
countNameservers=$(grep -c nameserver /etc/resolv.conf)
echo "Total ${countNameservers} nameservers defined in ${file}"
break
fi
done
Early continuation with continue statement
To resume the next iteration of the enclosing FOR, WHILE or UNTIL loop use continue statement.
for I in 1 2 3 4 5
do
statements1 #Executed for all values of ''I'', up to a disaster-condition if any.
statements2
if (condition)
then
continue #Go to next iteration of I in the loop and skip statements3
fi
statements3
done
This script make backup of all file names specified on command line. If .bak file exists, it will skip the cp command.
#!/bin/bash
FILES="$@"
for f in $FILES
do
# if .bak backup file exists, read next file
if [ -f ${f}.bak ]
then
echo "Skiping $f file..."
continue # read next file and skip cp command
fi
# we are hear means no backup file exists, just use cp command to copy file
/bin/cp $f $f.bak
done
# Cheat Keys
Source: http://www.linuxtopia.org/online_books/advanced_bash_scripting_guide/fto.html
!! - Last command
!foo - Run most recent command starting with 'foo...' (ex. !ps, !mysqladmin)
!foo:p - Print command that !foo would run, and add it as the latest to
command history
!$ - Last 'word' of last command ('/path/to/file' in the command 'ls -lAFh
/path/to/file', '-uroot' in 'mysql -uroot')
!$:p - Print word that !$ would substitute
!* - All but first word of last command ('-lAFh /path/to/file' in the command
'ls -lAFh /path/to/file', '-uroot' in 'mysql -uroot')
!*:p - Print words that !* would substitute
^foo^bar - Replace 'foo' in last command with 'bar', print the result, then
run. ('mysqladmni -uroot', run '^ni^in', results in 'mysqladmin -uroot')
{a,b,c} passes words to the command, substituting a, b, and c sequentially
(`cp file{,.bk}` runs `cp file file.bk`)
Ctrl + a - Jump to the start of the line
Ctrl + b - Move back a char
Ctrl + c - Terminate the command
Ctrl + d - Delete from under the cursor
Ctrl + e - Jump to the end of the line
Ctrl + f - Move forward a char
Ctrl + k - Delete to EOL
Ctrl + l - Clear the screen
Ctrl + r - Search the history backwards
Ctrl + R - Search the history backwards with multi occurrence
Ctrl + t - Transpose the current char with the previous
Ctrl + u - Delete backward from cursor
Ctrl + w - Delete backward a word
Ctrl + xx - Move between EOL and current cursor position
Ctrl + x @ - Show possible hostname completions
Ctrl + z - Suspend/ Stop the command
Ctrl + x; Ctrl + e - Edit line into your favorite editor
Alt + < - Move to the first line in the history
Alt + > - Move to the last line in the history
Alt + ? - Show current completion list
Alt + * - Insert all possible completions
Alt + / - Attempt to complete filename
Alt + . - Yank last argument to previous command
Alt + b - Move backward
Alt + c - Capitalize the word
Alt + d - Delete word
Alt + f - Move forward
Alt + l - Make word lowercase
Alt + n - Search the history forwards non-incremental
Alt + p - Search the history backwards non-incremental
Alt + r - Recall command
Alt + t - Transpose the current word with the previous
Alt + u - Make word uppercase
Alt + back-space - Delete backward from cursor
(Here "2T" means Press TAB twice)
$ 2T - All available commands(common)
$ (string)2T - All available commands starting with (string)
$ /2T - Entire directory structure including Hidden one
$ (dir)2T - Only Sub Dirs inside (dir) including Hidden one
$ *2T - Only Sub Dirs inside without Hidden one
$ ~2T - All Present Users on system from "/etc/passwd"
$ $2T - All Sys variables
$ @2T - Entries from "/etc/hosts"
$ =2T - Output like ls or dir
.bash_profile = sourced by login shell,
.bashrc = sourced by all shells,
.bash_aliases = should be sourced by .bashrc
Run something:
for i in a b c; do $i 'hello'; done
Do something on a bunch of files:
for i in *.rb; do echo "$i"; done
If syntax:
if [[ -e .ssh ]]; then echo "hi"; fi
Numerical comparison:
i=0; if (( i <= 1 )); then echo "smaller or equal"; else echo "bigger"; fi
file check flags:
-e: file exists
-f: regular file (non directory)
-d: directory
-s: non-zero file
-x: execute permission
Avoid duplicates in your history:
export HISTIGNORE="&:ls:ls *:[bf]g:exit"
이메일로 전송BlogThis!Twitter에서 공유Facebook에서 공유
라벨:
Informatics
- split a string into charaters
- read a given line
- sort by tab and numeric
- table merge
- array index
- loop
- cheat keys
sort -t$'\t' --key 8,8 --key 3,3n --key 12,12 --key 9.9 --key 1,1
paste -d , date1.csv date2.csv
Scientist. Husband. Daddy. --- TOLLE. LEGE
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