08-10-2011
Shell if with no parens takes a single command execution string, possibly piped and subshell'd (), and a $? of 0 is true, like "if grep -q haha logfile ; then . . . ." The $? is from the last command, as I recall, so "if find . -type f|grep -q .profile ; then . . . ." tests the exit() value of grep and "if ( find . -type f >/tmp/myfiles ; grep -q .profile /tmp/myfiles ); then . . . ." also tests grep. (An extra fork() and named file open twice is probably more expensive than a pipe() call, slower because of latency and leaves a file behind.)
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Hi
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to
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hi, unix gurus.
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I have done a great deal of research on this and still cannot come to an understanding of the following:
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Hi,
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Hi.could you explain me what are the rules when we are using double parentesis in if statement,if I put ,the code is working ,with (( is not
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then
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then
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ZGREP(1) General Commands Manual ZGREP(1)
NAME
zgrep - search possibly compressed files for a regular expression
SYNOPSIS
zgrep [ grep_options ] [ -e ] pattern filename...
DESCRIPTION
Zgrep invokes grep on compressed or gzipped files. These grep options will cause zgrep to terminate with an error code:
(-[drRzZ]|--di*|--exc*|--inc*|--rec*|--nu*). All other options specified are passed directly to grep. If no file is specified, then the
standard input is decompressed if necessary and fed to grep. Otherwise the given files are uncompressed if necessary and fed to grep.
If the GREP environment variable is set, zgrep uses it as the grep program to be invoked.
EXIT CODE
2 - An option that is not supported was specified.
AUTHOR
Charles Levert (charles@comm.polymtl.ca)
SEE ALSO
grep(1), gzexe(1), gzip(1), zdiff(1), zforce(1), zmore(1), znew(1)
ZGREP(1)