Location and special variables for bash programming under Linux (iv)

Location and special variables for bash programming under Linux (iv)

1.bash Position Variable:

$, $, ... The 1th parameter, the second argument, ...

Shift poll substitution, culling

Example: Using a script to interpret the meaning of positional variables, create the following script:

Nano shift.sh Create a script file and add the following:

#!/bin/bash

#

If [$#-lt 5]; Then the script is followed by no less than 5 parameters

echo "./shift.sh ARG1 .... ARG5 "

Exit 5

Fi

echo "args:$1 $ $4 $" shows 1th to 5th parameters respectively

ECHO Displays the first parameter after the script

#shift Note, default forward culling of 1 parameters

Shift 2 rejects 2 parameters, 3rd parameter changes to 1th parameter

echo $ shows the 1th argument behind the script, which is actually the 3rd parameter of the script

Shift 2 rejects 2 parameters, 5th parameter changes to 1th parameter

echo $ shows the 1th argument behind the script, which is actually the 5th parameter of the script

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./shift 1 2 3 4 5 execution results are shown below

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2.bash Special variables:

$?: Execution status Code return value

$#: Number of parameters

$*: Parameter list

[email protected]: parameter list

Example: Create a script, followed by at least one parameter, and display the number of parameters and list, or exit the script

Vim special.sh Creating a script file

#!/bin/bash

#

If [$#-lt 1]; Then

echo "usage:./special.sh ARG1 [ARG2 ...]"

Exit 9

Fi

echo "\$# is $#" displays the number of parameters

echo "\$* is $*" list

echo "\[email protected] is [email protected]" list

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chmod a+x special.sh granted execution rights

./special/etc/passwd/etc/shadow/proc

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3. File test:

-e file: Test files exist

-F File: Test files are normal files

-D FILE: Tests whether the specified path is a directory

-R File: Tests whether the current user has read access to the specified file;

-W File: Tests whether the current user has write access to the specified file;

-X file: Tests whether the current user has execute permission on the specified file;

4. Script Exit command

Exit n N uses 0-255 exit status code value

PS: If the script does not explicitly define the exit status code, then the exit code of the last command executed is the exit status code of the script;

Example: Specify a file: If it is a normal file, it will display files, if it is a directory, display directory;

Otherwise, this is an unrecognized file; Please create such a script file

Vim exist.sh Creating a script file

#!/bin/bash

File=/etc/rc.d/rc.sysinit

if [!-e $FILE]; Then determine if the file exists

echo "NO such $FILE"

Exit 88 does not exist exit current script, exit code is 88, can write freely between 0-255

Fi

If [-f $FILE]; Then determine whether the file

echo "$FILE is FILE"

elif [-D $FILE]; Then determine if the directory

echo "$FILE is directory"

Else

echo "I don't known this $FILE" file not known

Fi

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5. Test Scripts

Bash-n Script syntax error checking:

Bash-x script: Stepping through steps

Bash-x exist.sh test Script execution steps

This article is from the "Xavier Willow" blog, please be sure to keep this source http://willow.blog.51cto.com/6574604/1763764

Location and special variables for bash programming under Linux (iv)