File and Content Processing - cat, tac
1. cat: Display file content
Functional description of cat command
The cat command is used to connect multiple files and print to screen output or redirect to a specified file
Grammatical Format of cat Command
cat [OPTION]... [FILE]...
cat [-AbeEnstTuv] [--help] [--version] fileName
Option description of file command
There are many cat parameters, but only a few are used. Table 1 shows the parameters and descriptions of the cat command:
Table 1: Parameters and description of cat command
| Parameter options | interpretative statement |
|---|---|
| - n or -- number | Number all output lines starting from 1. |
| - b or -- number-nonblank | Similar to - n, except that blank lines are not numbered. |
| - s or -- squeeze-blank | When there are more than two blank lines in a row, replace them with blank lines in a row. |
| - v or -- show-nonprinting | Use ^ and M - symbols, except for LFD and TAB. |
| - E or -- show-ends | Display $at the end of each line. |
| - T or -- show-tabs | Display the TAB character as ^ I. |
| -A, --show-all | Equivalent to - vET. |
| -e | Equivalent to the "-vE" option; |
| -t | Equivalent to the "-vT" option; |
Practical operation of cat command
Example 1: Execute the complete command of the cat command to generate the contents of the oldboy.txt file and view the contents without parameters
-------------------------------------------------------------- ==>The order is as follows<== -------------------------------------------------------------- cat >oldboy.txt <<EOF I Love Linux Me too good EOF -------------------------------------------------------------- ==>The demonstration is as follows<== -------------------------------------------------------------- [root@oldboyedu /test]# ls [root@oldboyedu /test]# cat >oldboy.txt <<EOF > I Love Linux > > Me too >good > EOF [root@oldboyedu /test]# ls oldboy.txt -------------------------------------------------------------- ==>View content without parameters<== -------------------------------------------------------------- [root@oldboyedu /test]# cat oldboy.txt I Love Linux Me too good
Example 2: Execute the cat command with - n and - b options, and compare the differences
--------------------------------------------------------------
==>-n Print line numbers, including blank lines<==
--------------------------------------------------------------
[root@oldboyedu /test]# cat -n oldboy.txt
1 I Love Linux
2
3 Me too
4
5 good
--------------------------------------------------------------
==>-b Line numbers are printed, but blank lines are not included.<==
--------------------------------------------------------------
[root@oldboyedu /test]# cat -b oldboy.txt
1 I Love Linux
2 Me too
3 goodExample 4: Execute the cat command with the - E parameter
[root@oldboyedu /test]# cat -E oldboy.txt I Love Linux$ $ Me too$ $ good$ -------------------------------------------------------------- ==>End identifier $，Even empty lines should be displayed $<== -------------------------------------------------------------- [root@oldboyedu /test]# echo >oldboy1.txt [root@oldboyedu /test]# cat -E oldboy1.txt $ [root@oldboyedu /test]# ll oldboy1.txt -rw-r--r-- 1 root root 1 4 Month 1415:18 oldboy1.txt
Example 5: Execute the cat command with - s parameters
-------------------------------------------------------------- ==>A few additional lines of text<== -------------------------------------------------------------- [root@oldboyedu /test]# cat >>oldboy.txt <<EOF > > > if you like my blog > > > call me qq > EOF -------------------------------------------------------------- ==>give the result as follows<== -------------------------------------------------------------- [root@oldboyedu /test]# cat oldboy.txt I Love Linux Me too good if you like my blog call me qq -------------------------------------------------------------- ==>-s The effect is as follows<== -------------------------------------------------------------- [root@oldboyedu /test]# cat -s oldboy.txt I Love Linux Me too good if you like my blog call me qq
2. tac: Reverse display of file content
Functional description of tac command
tac is the reverse spelling of cat, so the function of the command is to display the file content in reverse.
Grammatical Format of cat Command
tac [OPTION]... [FILE]...
tac [-AbeEnstTuv] [--help] [--version] fileName
Option description of tac command
tac is not used much, just a brief understanding here.
Example 1: View text content in reverse order
-------------------------------------------------------------- ==>Write text in a document<== -------------------------------------------------------------- [root@oldboyedu /test]# echo "1234567" >> oldboy3.txt [root@oldboyedu /test]# echo "1234567" >> oldboy3.txt [root@oldboyedu /test]# echo "1111111" >> oldboy3.txt [root@oldboyedu /test]# echo "2222222" >> oldboy3.txt [root@oldboyedu /test]# echo "3333333" >> oldboy3.txt -------------------------------------------------------------- ==>Normal view<== -------------------------------------------------------------- [root@oldboyedu /test]# cat oldboy3.txt 1234567 1234567 1111111 2222222 3333333 -------------------------------------------------------------- ==>Reverse lookup<== -------------------------------------------------------------- [root@oldboyedu /test]# tac oldboy3.txt 3333333 2222222 1111111 1234567 1234567 [root@oldboyedu /test]#
So far as I'm concerned, if you have any questions or mistakes, please feel free to comment on them.