Shell Programming (i)

Variable:

1. Variable declaration eg:

#:name= ' EKO '

#!/bin/bashMyurl="http://www.w3cschool.cc"readonly myurl      / /declare read-only variables

2. Variables using eg:

#:echo $name #: Echo ${name}  

3. Delete variables eg:

#: Uset Name

4. Variable type:

• Local variables Eg:

#:local name= ' Eko '

• environment variables Eg:

#:export name= ' EKo '

5. View variables

#:printenv     //View all current environment variables #:set         //View all current variables

Format:

The first line of the shell script must be #! /bin/bash

Conditional judgment: (integer comparison, character comparison, file judgment)

An expression:

[Expression] [[expression]] test expression

Branch statements:

Branch statement if  judgment condition then    statement1    statement2 ...    else    ... fi multi-branch if  judging condition then    statement1    statement2    elif    statement1    statement2    ... else    statement1    statement2    ...      Fi

　　

Integer comparison:

-EQ: Determine if the value equals eg: # [$a-eq $b]  returns equal to 1  unequal return 0-ne: Determines whether the value equals eg: # [$a-ne $b]  returns 0  unequal return 1-GT: greater than judgment-LT: small To judge-ge: greater than or equal to-le: less than or equal to

Example: Determine file size if larger than 100 lines output large file otherwise output small file

#!/bin/bashlines= ' wc/etc/passwd ' echo $LINESNEWLINES = ' echo $LINES | cut-d '-f1 ' [$NEWLINES-gt] && echo ' This is big file ' | | Echo ' This is small file '

Or

#!/bin/bashfile_path= '/home/eko/passwd ' if [' Wc-l $FILE _path | cut-d '-f1 '-gt ']then echo ' This is big FILE ' else E Cho ' This is small file ' fi

File test

-e filename  if filename exists, true  [-e/var/log/syslog]-d filename  if filename is directory, true  [-d/tmp/mydir]-f fi Lename  True if filename is a regular file  [-f/usr/bin/grep]-l filename  If filename is a symbolic link, true  [-l/usr/bin/grep]-r FileName  If filename is readable, true  [-r/var/log/syslog]-w filename  If filename is writable, true  [-w/var/mytmp.txt]- x filename  If filename is executable, true  [-l/usr/bin/grep]filename1-nt filename2  If filename1 is newer than filename2, true c15/>[/tmp/install/etc/services-nt/etc/services]filename1-ot filename2  If filename1 is older than filename2, then true  [/ Boot/bzimage-ot Arch/i386/boot/bzimage]

　

#shell判断文件夹是否存在 #如果文件夹不存在, create a folder if [!-D "/top"]; Then mkdir-p/TOPFI #shell判断文件 whether the directory exists or has permissions folder= "/top" file= "/top/test.txt" #-x parameter to determine if the $folder exists and has enforceable permissions if [!-X "$folder"]; Then mkdir the "$folder" FI #-D parameter to determine if the $folder exists if [!-D "$folder"]; Then mkdir the "$folder" FI #-F parameter to determine if $file exists if [!-F "$file"]; Then touch "$file" fi#-N to determine if a "variable" has a value if [!-n "$file"]; Then echo "$file variable is empty! "Exit 0fi # Determines if the string contents of two variables are the same if [" $file 1 "=" $file 2 "]; Then echo ' $file 1 equal $file 2 "Else echo" $file 1 Not equal $file 2 "fi

Exit script

Exit [Status Code]: Exit Script

If no status code is specified, then the status code of the last command executed is the exit status code

Positional Parameters/Special parameters

#!/bin/bashecho "First argument is $" echo "second argument is"

$: First parameter

$ A: The second parameter

...

$#: Number of parameters

$*: Parameter list

[email protected]: parameter list

[Email protected]:~$/test.sh First Secondfirst argument is Firstsecond argument

　　

Shell Programming (i)