String Manipulation 字串處理

字串長度

my_string="abhishek"
echo "length is ${#my_string}"

Using expr

str="my string"
length=$(expr length "$str")
echo "Length of my string is $length"

Using awk

echo "my string" | awk '{print length}'

Using wc

str="my string"
length=$(echo -n "my string" | wc -m)
echo "Length of my string is $length"

字串比對

Using wildcards

#!/bin/bash

STR='GNU/Linux is an operating system'
SUB='Linux'
if [[ "$STR" == *"$SUB"* ]]; then
  echo "It's there."
fi

Using case

#!/bin/bash

STR='GNU/Linux is an operating system'
SUB='Linux'

case $STR in

  *"$SUB"*)
    echo -n "It's there."
    ;;
esac

Using Regex

#!/bin/bash

STR='GNU/Linux is an operating system'
SUB='Linux'

if [[ "$STR" =~ .*"$SUB".* ]]; then
  echo "It's there."
fi

Using Grep

#!/bin/bash

STR='GNU/Linux is an operating system'
SUB='Linux'

if grep -q "$SUB" <<< "$STR"; then
  echo "It's there"
fi

字串合併

str1="hand"
str2="book"
str3=$str1$str2

字元提取

foss="Fedora is a free operating system"
echo ${foss:0:6}

_admin_ip="202.54.1.33|MUM_VPN_GATEWAY 23.1.2.3|DEL_VPN_GATEWAY 13.1.2.3|SG_VPN_GATEWAY"
for e in $_admin_ip
do
   ufw allow from "${e%%|*}" to any port 22 proto tcp comment 'Open SSH port for ${e##*|}'
done

字元取代

foss="Fedora is a free operating system"
echo ${foss/Fedora/Ubuntu}

Summary: String Manipulation and Expanding Variables

${parameter:-defaultValue}	Get default shell variables value
${parameter:=defaultValue}	Set default shell variables value
${parameter:?"Error Message"}	Display an error message if parameter is not set
${#var}	Find the length of the string
${var%pattern}	Remove from shortest rear (end) pattern
${var%%pattern}	Remove from longest rear (end) pattern
${var:num1:num2}	Substring
${var#pattern}	Remove from shortest front pattern
${var##pattern}	Remove from longest front pattern
${var/pattern/string}	Find and replace (only replace first occurrence)
${var//pattern/string} echo "${PATH//:/$'\n'}"	Find and replace all occurrences
${!prefix*}	Expands to the names of variables whose names begin with prefix.
${var,} ${var,pattern}	Convert first character to lowercase.
${var,,} ${var,,pattern}	Convert all characters to lowercase.
${var^} ${var^pattern}	Convert first character to uppercase.
${var^^} ${var^^pattern}	Convert all character to uppercase.

Cheatsheet: String Manipulation

String To Integer

# $((string))
sum=$((3+6))
echo $sum

a=11
b=3
c=$(($a+$b))
echo $c

Alternate method: expr

Note that it is not a “native” Bash procedure, as you need to have coreutils installed (by default on Ubuntu) as a separate package.

a=5; b=3; c=2; d=1
expr $a + $b \* $c - $d

去除變數的末端字元 .XXX

# Operator "#" means "delete from the left, to the first case of what follows."
x="This is my test string."
echo ${x#* }

is my test string.

# Operator "##" means "delete from the left, to the last case of what follows."
x="This is my test string."
echo ${x##* }

string.

# Operator "%" means "delete from the right, to the first case of what follows."
x="This is my test string."
echo ${x% *}

This is my test

# Operator "%%" means "delete from the right, to the last case of what follows."
x="This is my test string."
$ echo ${x%% *}

This