Redirection (computing): Difference between revisions

Revision as of 15:47, 15 September 2020

Revision as of 05:03, 17 September 2020

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===Basic===

Typically, the [[syntax]] of these characters is as follows, using <code>&lt;</code> to redirect input, and <code>&gt;</code> to redirect output. <syntaxhighlight lang="bash" inline>command1command > file1</syntaxhighlight> executes {{mono|command1}}, placing the output in {{mono|file1}}, as opposed to displaying it at the terminal, which is the usual destination for standard output. This will [[Clobbering|clobber]] any existing data in {{mono|file1}}.

Using <syntaxhighlight lang="bash" inline>command1command < file1</syntaxhighlight> executes {{mono|command1}}, with {{mono|file1}} as the source of input, as opposed to the [[Computer keyboard|keyboard]], which is the usual source for standard input.

<syntaxhighlight lang="bash" inline>command1command < infile > outfile</syntaxhighlight> combines the two capabilities: {{mono|command1}} reads from {{mono|infile}} and writes to {{mono|outfile}}

===Variants===

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To read from a stream literal (an inline file, passed to the standard input), one can use a [[here document]], using the <code>&lt;&lt;</code> operator:

<syntaxhighlight lang="bashconsole">

$ tr a-z A-Z << END_TEXT

> one two three

> uno dos tres

> END_TEXT

ONE TWO THREE

UNO DOS TRES

</syntaxhighlight>

To read from a string, one can use a [[here string]], using the <code>&lt;&lt;&lt;</code> operator: <syntaxhighlight lang="bash" inline>tr a-z A-Z <<< "one two three"</syntaxhighlight>, or:

<syntaxhighlight lang="bashconsole">

$ NUMBERS="one two three"

$ tr a-z A-Z <<< "$NUMBERS"

ONE TWO THREE

</syntaxhighlight>