Shell Programming (ii)

Bo main name: Li Changming

Post Address: http://keep88.blog.51cto.com

This note is from the old boy books: Learn Linux OPS Shell programming with old boys

The advanced and practice of shell variable knowledge

1. Special positional parameter variables in the shell:

	& nbsp             role description
$0
$n	n=1..9   gets the nth parameter value of the currently executing shell script, n is 0 o'clock, the output script file name, n>9, must be enclosed in curly braces, such as ${10}
$#
$*
[email protected]	Gets the arguments for all parameters of the current shell script, and if [email protected] is given a double quote, "[email protected]" treats all parameters as separate strings, such as "$", "$"   "$ $" ...

For example:

1), $n use: N is {1..15}

Tips: [[email protected] test]# echo \${1..15}$1 $2 $3 $4 $5 $6  $7 $8 $9 $10 $11 $12 $13 $14 $15  [[email  Protected] test]# echo \a{1..10}a1 a2 a3 a4 a5 a6 a7 a8  a9 a10        #>==  Use this technique to quickly output a regular string  [[email  protected] test]# pwd/root/test[[email protected] test]# vim t1.sh [[ email protected] test]# cat t1.sh echo $1[[email protected] test]#  sh t1.sh  testtest[[email protected] test]# sh t1.sh   Zhangsan  lisizhangsan[[email protected] test]# vim t1.sh[[email protected]  test]# cat t1.sh echo $1 $2 $3[[email protected] test]# sh  t1.sh zhangsan wangwu lisizhangsan wangwu lisi 

Be aware that:

When the argument is greater than 9 o'clock, it must be enclosed in curly braces with ${10} ${11} ${12}.....${15}

2), the use of $ A:

[[email protected] test]# vim T2.sh[[email protected] test]# cat t2.sh echo $0[[email protected] test]# sh t2.sht2.sh[[ema Il protected] test]# sh t2.sh zhangsant2.sh Note: List two commands using 1), DirName and basename dirname: Get path basename: Acquired Fetch file name [[email protected] test]# dirname/root/test/t1.sh/root/test [[email protected] test]# basename/root/ Test/t1.sh t1.sh

3), $ #的使用:

[Email protected] test]# vim t2.sh [[email protected] test]# cat t2.sh echo $#[[email protected] test]# sh t2.sh zhangsan Lisi Wangwu Test1 Test25

4), $* [email protected] "$*" "[email protected]" The difference:

Combining the above concepts, examples of these four differences are analyzed:

1), use set to set positional parameters (same as command line script) [[email protected] ~]# set --  "I am"  smart  Boy. [[email protected] ~]# echo $ #3 [[email protected] ~]# echo $1i am [[email protected] ~]# echo $2smart[[email protected] ~]# echo $3boy.2 ), Test $* and [email protected], without double quotes [[Email protected] ~]# echo $*i am smart  boy. [[email protected] ~]# echo [email protected]i am smart  Boy. Use the For loop to output all parameters:   [[email protected] ~]# for i in $*;d O echo   $i;d Oneiamsmartboy. [[email protected] ~]# for i in [email protected];d o echo  $i; doneiamsmartboy.3), test "$*"   and   "[email protected]"  , note the use of double quotation marks [[email protected] ~]#  echo  "$*" I am smart boy. [[email protected] ~]# echo  "[Email&nbsP;protected] "I am smart boy. Use for output all parameters:[[email protected] ~]# for i  in  "$*";d o echo  $i;d onei am smart boy. [[email protected] ~]# for i in  "[email protected]";d o echo  $i; Donei amsmartboy. Summary:   Review at the beginning we wrote the concept analysis:   $* and [email protected] without quotes, output all parameters, in the For statement, If there is a space-delimited string, the split output   $* and [email protected] are quoted, with the example "$*"   "[email protected]", at which point the difference:     $*  will have all parameters as the full string output, as shown above     [email protected]  will all parameters, As a standalone single character output, if there is a space-delimited string, the output is not split as a separate single character output. Comment:  set  and eval commands in detail:   set can be used as command line   eval command: First scan the command line for all permutations before executing the command. This command applies to variables that scan for a time that does not function. This command scans the variable two times. These variables, which need to be scanned two times, are sometimes referred to as complex variables    for example: [[email protected] ~]# a= "cat t1.sh" [[email  protected] ~]# echo  $Acat  t1.sh[[email protected] ~]# eval  $A  #>==   the eval command now displaces the variable and executes the command i am smart  Boy.set with the use of Eval, the example used in scripting: Example 1), [[Email protected] ~]# number=$ (Set -- $ (cat  t4.sh); eval  "echo \$$#") Comment:  set  set incoming parameters,     eval perform two scans,   $#: Outputs the total number of positional parameters,          $$#: The total number, which is the value of the last positional parameter, Assign a value to number[[email protected] ~]# echo  $Number 5 cases 2), [[email protected] ~]#  runleveln 5[[email protected] ~]# runlevel=$ (set -- $ (Runlevel);eval  "Echo  \$$# ") [[email protected] ~]# echo  $Runlevel 5

2. Special state variables in the shell process:

$? Gets the execution state return value that executes the last instruction (0 for success, not 0 for failure)

3. Bash shell built-in variable command:

1), echo parameter

echo parameter options
-n
-e	Parsing escape character
transfer character:
\n	newline
\t	tab
\r	enter
\b	backspace
\v	portrait tab

2), eval command use

[[email protected] ~]# cat T1.shecho \$$#[[email protected] ~]# sh t1.sh arg1 arg2$2 #>== $#: Total output position parameters 2 $$#:$2 echo Output

[[email protected] ~]# cat t1.sh eval echo \$$# #>== add eval command to output echo $ with command [[email protected] ~]# sh t1.sh arg1 Arg2 Arg3 Arg4arg4

3), shift

The main function of the shift command is to move the position parameter $1,$2, such as left, that is, if the position parameter is $3,$2,$1, then after a shift is performed, the $ $2,$2 becomes the $1,$1 and disappears.

For example:

[email protected] ~]# cat t4.sh echo $ $2if [$#-eq 2];then shift echo $1;fi[[email protected] ~]# sh t4.sh arg1 arg 2arg1 arg2arg2 #>== After the shift command is executed, the arg1 is left out, leaving the new $ $, which is arg2

4. Shell variable string knowledge and practice

An expression	Description
${parameter}	Returns the contents of the variable $parameter
${#parameter}	Returns the length of the variable $parameter content
${parameter:offset}	In variable ${parameter}, start extracting string to end after offset from position
${parameter:offset:length}	In Variable ${parameter}, a string of length is extracted from the position offset after
${parameter#word}	Delete the shortest matching word string from the beginning of the variable ${parameter}
${parameter# #word}	Delete the longest matching word string from the beginning of the variable ${parameter}
${parameter%word}	Delete the shortest matching word string starting at the end of the variable ${parameter}
${parameter%%word}	Delete the longest matching word string starting at the end of the variable ${parameter}
${parameter/pattern/string}	Use a string instead of the first matching pattern
${parameter//pattern/string}	Use string instead of all matching pattern

Examples illustrate the use of built-in variables:

1), ${#parameter}: Calculated length

[Email protected] ~]# name= "lichangming" [[email protected] ~]# echo ${#name}11 #>== exactly 11 characters "lichangming"

2), ${parameter:offset}: Extracts the content to the end after the specified position, similar to the tiles in Python

[Email protected] ~]# name= "lichangming" [[email protected] ~]# echo ${name:3}hangming[[email protected] ~]# echo ${name: 2}changming

3), ${parameter:offset:length}: Start extracting string length from position offset

[[email protected] ~]# name= "lichangming" [[email protected] ~]# echo ${name:2:7}changmi #>== output 2nd position after 7th position content

Note:

The method of intercepting content on this, with the function of the CUT-C command

For example:

[[email protected] ~]# echo $namelichangming [[email protected] ~]# echo ${name} | Cut-c 2-7ichang #>== Cut command, followed by a number indicating: intercept the character of the 2~7 position and the difference between the built-in variable, the first offset of the built-in variable, the starting position is the content after offset

4), ${parameter#word}: Delete the shortest matching word string from the beginning

[[email protected] ~]# echo $namelichangming [[email protected] ~]# echo ${name#l*g}ming #>== matches the L to G string, remove it, note that it must be from the beginning Start matching, shortest match [[email protected] ~]# echo ${name#c*g}lichangming #>==c not match from the beginning, so no match found, no delete, output all

5), ${parameter# #word}: Delete the longest match from the beginning

[Email protected] ~]# name= "lichangmingcming" [[email protected] ~]# echo $namelichangmingcming [[email protected] ~]# echo ${name# #l *c}ming #>== longest match, matching LICHANGMINGC, deleting it, leaving Ming to see the results of the shortest match deletion: [[email protected] ~]# echo ${name#l*c} Hangmingcming #>== shortest match, matching lic, deleting

All of the above matching deletions are removed from the beginning.

6), ${parameter%word}: Delete shortest match from end

7), ${parameter%%word}: Delete longest match from end

For example:

[[email protected] ~]# echo $namelichangmingcming [[email protected] ~]# echo ${name%i*g}lichangmingcm[[email protected] ~]# echo ${name%%i*g}l[[email protected] ~]# echo ${name%%c*m}lichangmingcming[[email protected] ~]# echo ${name%%m*g} Lichang

Attention:

From the end of the match, refers to the first value and the end of the G-range string, in the above example, C*m, beginning with C, the middle is any value, the end is M, then did not find a matching result, output all, so, must remember is the first value and the end of the match.

8), ${parameter/pattern/string}: replace string with first match pattern

[Email protected] ~]# name= "Li2chang3ming4hehe8" [[email protected] ~]# echo $nameli 2chang3ming4hehe8[[email protected ] ~]# Echo ${name/3*4/test}li2changtesthehe8

9), ${parameter//pattern/string}: Replace string with all matching patterns pattern

[Email protected] ~]# name= "Zhangsan Lisi Wangwu Zhangsan liming" [[email protected] ~]# echo $namezhangsan Lisi Wangwu zh Angsan Liming[[email protected] ~]# echo ${name//zhangsan/someone}someone Lisi Wangwu someone liming

Note:

Use the method above to modify the file name in bulk

1), Generate test files:

[[email protected] test]# pwd/root/test[[email protected] test]# Ls[[email protected] test]# touch \smart_t{1..9}.sh[[ Email protected] test]# lssmart_t1.sh smart_t3.sh smart_t5.sh smart_t7.sh smart_t9.shsmart_t2.sh smart_t4.sh smart_t 6.sh smart_t8.sh

Batch rename: Change smart_t*.sh to Silly_t*.sh

[Email protected] test]# lssmart_t1.sh smart_t3.sh smart_t5.sh smart_t7.sh smart_t9.shsmart_t2.sh smart_t4.sh Smart _t6.sh Smart_t8.sh[[email protected] test]# for i in ' ls *.sh ';d o mv $i ' echo ${i//smart/silly} '; Done[[email protected] test]# lssilly_t1.sh silly_t3.sh silly_t5.sh silly_t7.sh silly_t9.shsilly_t2.sh silly_t4.sh s Illy_t6.sh silly_t8.sh

This method is the method of renaming that is implemented using a string substitution of variables.

2), rename with rename command:

[Email protected] test]# rename "smart" "silly"/root/test/*.sh[[email protected] test]# lssilly_t1.sh silly_t3.sh sil ly_t5.sh silly_t7.sh silly_t9.shsilly_t2.sh silly_t4.sh silly_t6.sh silly_t8.sh

3), for loop combined with SED for batch renaming:

[Email protected] test]# lssilly_t1.sh silly_t3.sh silly_t5.sh silly_t7.sh silly_t9.shsilly_t2.sh silly_t4.sh Silly _t6.sh Silly_t8.sh[[email protected] test]# for i in ' ls *.sh ';d o mv $i ' echo $i | Sed s/silly/smart/g ';d one[[email protected] test]# lssmart_t1.sh smart_t3.sh smart_t5.sh smart_t7.sh Smart_t9.shsmart_ t2.sh smart_t4.sh smart_t6.sh smart_t8.sh

This article is from the "Keep Keep your" blog, be sure to keep this source http://keep88.blog.51cto.com/11829099/1930977

Shell Programming (ii)