IO redirection and piping on Linux-&> &>> 2> 2>> 2>&1 2>>&1 | Tee TR

IO redirection:

Output REDIRECT:>

features: Overwrite output

Output REDIRECT:>>

Features: Append output

# set-c

suppresses overwrite output redirection to existing files;

You can use the force overwrite output at this time: >|

# set +c

Turn off the above features

Error output stream redirection: 2> 2>> will only output the wrong information to the specified location

merge Normal output stream and error output stream:

(1) &>, &>>

(2) COMMAND >/path/to/somefile 2>&1

COMMAND >>/path/to/somefile 2>&1

[[email protected] tmp]# Ech "Next" > A.txt-bash:ech:command not found[[email protected] tmp]# ech "Next" > A.txt 2>&1[[email protected] tmp]# ech "Next" &> a.txt [[email protected] tmp]# Ech "Next" 2> a.txt

Special Equipment:/dev/null, representing empty

COMMAND >/dev/null: Represents all output information will not be displayed, go directly to the/dev/null inside

Use Demo:

[[email protected] tmp]# echo  "Hello"  > a.txt[[email protected] tmp ]# cat a.txt hello[[email protected] tmp]# echo  "Next"  >>  a.txt[[email protected] tmp]# cat a.txt hellonext[[email protected] tmp]#  ech  "Next"  > a.txt -bash: ech: command not found[[email  protected] tmp]# cat a.txt [[email protected] tmp]# ech  "Next"  2 > a.txt [[email protected] tmp]# cat a.txt -bash: ech: command  not found[[email protected] tmp]# ech  "Next"  &>> a.txt  [[email protected] tmp]# cat a.txt -bash: ech: command not  found-bash: ech: command not found[[email protected] tmp]# ech  "Next"  > /dev/null -bash: ech: command not found[[email protected] tmp]# ech  " Next " &> /dev/null

Enter redirection:

Enter redirect:<

Features: Overwrite input

Enter redirect:<<

Features: Append input

Use Demo:

1, [[email protected] tmp]# cat << EOF >a.txt> i> wish> nothing> but > the > best> for> yo  U>!> Eof[[email protected] tmp]# cat a.txt iwishnothingbut the bestforyou!2, [[email protected] tmp]# cat > A.txt << eof> l> o> v> e> eof[[email protected] tmp]# cat A.txt Love

TR command:

TR [OPTION] ... SET1 [SET2]

Converts the characters in the input data to the characters that appear in the SET1 definition, all the bits are converted to SET2 occurrences.

Usage 1:

TR SET1 SET2 </path/from/somefile

Usage 2:

Tr-d SET1 </path/from/somefile

Note: Do not modify the original file, only show it

[[email protected] tmp]# tr-d o < a.txt lve[[email protected] tmp]# cat a.txt love[[email protected] tmp]# tr "A-Z" "A -Z "< A.txt Love

Pipeline: A connection program that implements the output of the previous command directly after a program as an input data stream

COMMAND1 | COMMAND2 | COMMAND3 | ...

Converts the information in the first 6 lines of the/etc/passwd file into uppercase characters after output; [email protected] tmp]# Head-n 6/etc/passwd | Tr ' A-Z ' A-Z ' root:x:0:0:root:/root:/bin/bashbin:x:1:1:bin:/bin:/sbin/nologindaemon:x:2:2:daemon:/sbin:/sbin/ nologinadm:x:3:4:adm:/var/adm:/sbin/nologinlp:x:4:7:lp:/var/spool/lpd:/sbin/nologinsync:x:5:0:sync:/sbin:/bin/ SYNC

Tee command: Overwrites the results of the previous command to a file in a pipeline

[email protected] tmp]# Cat A.txt | Tee B.txtlove[[email protected] tmp]# cat B.txt Love

This article is from the "Wang Liming" blog, make sure to keep this source http://afterdawn.blog.51cto.com/7503144/1855782

IO redirection and piping on Linux-&> &>> 2> 2>> 2>&1 2>>&1 | Tee TR