Shell string Processing

Output the top 10 system user names and UID numbers of the current system to the screen
head/etc/passwd

String interception
1${variable name: Start position: Length}

echo ${variable name: Start position: Length}
Variable name =${variable name: Start position: Length}

806 Echo $HOSTNAME

808 ${hostname:0:3}
809 Echo ${hostname:0:3}
810 Echo $HOSTNAME
811 Echo ${hostname:0:5}
812 Domain=${hostname:0:5}
813 Echo $domain
814 Domain=${hostname:6}

2 Using expr substr
[Email protected] ~]# echo $HOSTNAME
Pc205.tarena.com
[Email protected] ~]#
[[email protected] ~]# expr substr "$HOSTNAME" 1 5
pc205
[[email protected] ~]# expr Length "$HOSTNAME"
16
[[email protected] ~]# expr Length "panglijing"
10
[Email protected] ~]#

3 Using the Cut tool
echo $var | Cut-b start position-end position
echo $HOSTNAME | Cut-b 1-5
echo $HOSTNAME | Cut-b 6-

Head-3/etc/passwd | Cut-d ":"-F 1,3

4 Path Segmentation
BaseName
DirName

[Email protected] ~]# Basename/etc/sysconfig/network-scripts/ifcfg-eth0
Ifcfg-eth0
[Email protected] ~]#
[Email protected] ~]#
[Email protected] ~]# BASENAME/ETC/PASSWD
passwd
[Email protected] ~]# basename/etc/sysconfig/network-scripts
Network-scripts
[Email protected] ~]# basename/etc/sysconfig/network-scripts
Network-scripts
[Email protected] ~]#

[Email protected] ~]# Dirname/etc/sysconfig/network-scripts/ifcfg-eth0
/etc/sysconfig/network-scripts
[Email protected] ~]#
[Email protected] ~]# dirname/etc/sysconfig/network-scripts
/etc/sysconfig
[Email protected] ~]#

+++++++++++++++++++++++++++++++++++++++++++++++++

String substitution
${var/old/new}
${var//old/new}

Name=panglijing
[[Email protected] Desktop]# echo ${name/i/f}
Panglfjing
[[Email protected] Desktop]# echo ${name//i/f}
Panglfjfng
[Email protected] Desktop]# echo $name
Panglijing
[[Email protected] Desktop]# newname=${name//i/f}
[Email protected] Desktop]# echo $newname
Panglfjfng
[[Email protected] Desktop]#

by condition Qiatouquwei
${var Replace symbol expression}
echo ${var replace symbol expression}
Variable name =${var replace symbol expression}

How expressions are represented
Wildcard characters
Normal characters
Wildcard characters + normal character

String deletion
Left-to-right, delete the data that matches the expression in the variable
# Shortest Match Delete
# # longest Match Delete

Right-to-left, delete data that matches the expression in a variable
% Shortest Match Delete
Percent of the longest match delete

825 Echo ${mail##*/}
826 mailbox=${mail##*/}
827 mailuser=${mail##*/}
828 echo $mailuser
829 Echo $MAIL
830 echo ${mail%/root}
831 Echo ${mail%/root}
832 echo $MAIL
833 Echo ${mail%/*}
----------------------------------------------------------------------
Get partial data for a string
----------------------------------------------------------------------
Assigning an initial value to a variable
${variable name symbol "value"}
echo ${variable name symbol "value"}
Variable name =${variable name symbol "value"}

--------------------------------------------------------------------
:=
${var:= "word"}
If the variable var already exists and is not NULL, the $var value is returned.
Otherwise, return the string "word" and assign a value to the variable var

---------------------------------------------------------------------
:+
${var:+ "word"}
If the variable var already exists and is not NULL, the string "word" is returned and a null value is returned instead.
Role: Determine whether a definition.

----------------------------------------------------------------------
:-
${var:-"word"}
If the variable var already exists and is not NULL, the value returned $var
Otherwise, the string "word" is returned, and the variable var value does not change.
----------------------------------------------------------------------
:?
${var:? ｝
${var:? "Word"}
If the variable var already exists and is not NULL, the value returned $var
, otherwise returns the string "word" and ends the script.
Function: The error caused by the output dependent variable not being defined.

#!/bin/bash
Read-p "Please input numbers" x
#x =${x:-"1"}
#y =${x:= "1"}
#y =${x:+ "1"}
Y=${x:?}
Echo ' $x is ' $x
Echo $y
---------------------------------------------------------------------
[email protected] shell]# cat check_veryone_ip.sh
#!/bin/bash
ip=${1:-"127.0.0.1"}
Ping-c 3 $ip &>/dev/null
If [$?-eq 0];then
Echo $ip is online
Else
Echo $ip is not online
Fi
[Email protected] shell]#

This article is from the Linux Cloud Computing blog, so be sure to keep this source http://liangzai818.blog.51cto.com/10003446/1763437

Shell string Processing