Special Command Symbols

Redirection

< file 

Reads input from the file file.

> file 

Writes standard output to the file file; i.e., an old file with the same name will be overwritten.

>> file 

Appends standard output to the file file; i.e., the information will be added at the end of the file file, if it already exists.

2> file 

Writes standard error to the file file.

&> file 

Writes standard output and error to the file file.

Example:

myprog <inputfile >outfile 2>errfile

The program myprog will read from the file inputfile and write its standard output to outfile and write error message to errorfile.

Command execution

; Separates multiple commands on the command line; i.e., the semi-colon corresponds to pressing ENTER between commands.

command1 ; command2 

is the same as

command1 command2

| Pipe symbol. Uses output from one command as input for the next command; i.e.,

command1 | command2

is the same as

command1 > outfile; command2 < outfile

Typing

!string 

repeats a previous command line that starts string.

echo $PATH ... !echo 

The last line corresponds to executing echo $PATH again.

Quotation

' ' (Single quotes) Quotes the enclosed string exactly.

Program=myprog
JobNr=1
OutputFile='${Program}_job$JobNr.out'
echo $OutputFile 

gives ${Program}_job$JobNr.out as output.

" " (Double quotes) Quotes the enclosed string after variable substitution.

Program=myprog
JobNr=1
OutputFile="${Program}_job$JobNr.out"
echo $OutputFile

gives myprog_job1.out as output

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Author: (LUNARC)

Last Updated: 2022-10-05