Bash shell string Truncation

Shell string truncation problem:
1. Linux shell intercepts the first eight characters of the character variable by using the following methods:
1. expr substr "$ a" 1 8
2. echo $ a | awk '{print substr (, 1, 8 )}'
3. echo $ a | cut-c1-8
4. echo $
5. expr $ :'\(.\\).*'
6. echo $ a | dd bs = 1 count = 8 2>/dev/null

2. truncate by specified string
1. Method 1:
$ {Varible # * string} captures the string after the last string from left to right.
$ {Varible # * string} captures the string after the first string from left to right.
$ {Varible % string *} captures the string after the last string from the right to the left
$ {Varible % string *} captures the string after the first string from the right to the left.
"*" Is only a wildcard.

Example:
$ Myvar1_foodforthought.jpg
$ Echo $ {MYVAR # * fo}
Rthought.jpg
$ Echo $ {MYVAR # * fo}
Odforthought.jpg

2. Method 2: $ {varible: n1: n2}: intercept the string from n1 to n2.

You can use another form of variable extension to select a special character string based on the specific character offset and length. Enter the following lines in bash:
$ EXCLAIM = cowabunga
$ Echo $ {EXCLAIM: 0: 3}
Cow
$ Echo $ {EXCLAIM: 3: 7}
Abunga

String Truncation in this form is very simple. You only need to use a colon to separate the start character and the length of the substring.

3. Split according to specified requirements:
For example, retrieve the prefix with the suffix removed.
Ls-al | cut-d "."-f1
For example, get the suffix
Ls-al | cut-d "."-f2

Here stringIt can be viewedHere documentIn additionCOMMAND <$ WORDAnd nothing else, De> $ WORD De> will be extended and sent De> COMMAND De>StdinMedium.

 

1 String = "This is a string of words ." 2 3 read-r-a Words <"$ String" 4 #-a option of the "read" command 5 # + the result values are allocated to each item in the array in order. 6 7 echo "First word in String is: $ {Words [0]}" # This 8 echo "Second word in String is: $ {Words [1]}" # is 9 echo "Third word in String is :$ {Words [2]}" # 10 echo "Fourth word in String is: $ {Words [3]}" # string 11 echo "th word in String is: $ {Words [4]}" # 12 echo "Sixth word in String is: $ {Words [5]}" # words. 13 echo "Seventh word in String is: $ {Words [6]}" # (null) 14 # $ String end. 15 16 # Thanks for Francisco Lobo's suggestion.

Example 17-13. Add text at the beginning of a file

1 #! /Bin/bash
2 # prepend. sh: Add text at the beginning of the file.
3 #
4 # example of the script donated by Kenny Stauffer,
5 # + The author of this article made a few modifications to this script.
6
7
8 E_NOSUCHFILE = 65
9
10 read-p "File:" file # 'read' command. The-p parameter is used to display the prompt.
11 if [! -E "$ file"]
12 then # If the file does not exist, come in.
13 echo "File $ file not found ."
14 exit $ E_NOSUCHFILE
15 fi
16
17 read-p "Title:" title
18 cat-$ file <$ title> $ file. new
19
20 echo "Modified file is $ file. new"
21
22 exit 0
23
24 # below is a section in 'Man bash:
25 # Here String
26 # here document:
27 #
28 # <word
29 #
30 # word is extended and provided to standard input of command.