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Shell Metacharacters

>

prog >file direct standard output to file

>>

prog >>file append standard output to file

<

prog <file take standard input from file

|

p1|p2 connect standard output of p1 to standard output of p2

<<str

here document: standard input follows, up to next str on a line by itself

*

match any string of zero or more characters in filenames

?

match any single character in filenames

[ccc]

match any single character from ccc in filenames; ranges like 0-9 or a-z are legal

;

command terminator: p1;p2 does p1, the p2

&

like ; but doesn't wait for p1 to finish

`...`

run command(s) in ...; output replaces `...`

(...)

run command(s) in ... in a sub-shell

{...}

run command(s) in ... in current shell (rarely used)

$1, $2 etc.

$0...$9 replaced by arguments to shell file

$var

value of shell variable var

${var}

value of var; avoids confusion when concatenated with text; see also Table 5.3

\

\c take character c literally, \newline discarded

'...'

take ... literally

"..."

take ... literally after $, `...`, and \ interpreted

#

if # starts word, rest of line is a comment (not in 7th Ed.)

var=value

assign to variable var

p1 && p2

run p1; if successful, run p2

p1 || p2

run p1; if unsuccessful, run p2