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Full Discussion: eval in shell scripting
Top Forums Shell Programming and Scripting eval in shell scripting Post 302197548 by mobydick on Wednesday 21st of May 2008 07:00:02 AM
Old 05-21-2008
eval in shell scripting

what is the real usage of eval in shell scripting

whats the difference between
$ cmd

&&
eval cmd
 

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GETFLAGS(8)						      System Manager's Manual						       GETFLAGS(8)

NAME
getflags, usage - command-line parsing for shell scripts SYNOPSIS
getflags $* usage [ progname ] DESCRIPTION
Getflags parses the options in its command-line arguments according to the environment variable $flagfmt. This variable should be a list of comma-separated options. Each option can be a single letter, indicating that it does not take arguments, or a letter followed by the space-separated names of its arguments. Getflags prints an rc(1) script on standard output which initializes the environment variable $flagx for every option mentioned in $flagfmt. If the option is not present on the command-line, the script sets that option's flag vari- able to an empty list. Otherwise, the script sets that option's flag variable with a list containing the option's arguments or, if the option takes no arguments, with the string 1. The script also sets the variable $* to the list of arguments following the options. The final line in the script sets the $status variable, to the empty string on success and to the string usage when there is an error parsing the command line. Usage prints a usage message to standard error. It creates the message using $flagfmt, as described above, $args, which should contain the string to be printed explaining non-option arguments, and $0, the program name (see rc(1)). If run under sh(1), which does not set $0, the program name must be given explicitly on the command line. EXAMPLE
Parse the arguments for leak(1): flagfmt='b,s,f binary,r res,x width' args='name | pid list' if(! ifs=() eval `{getflags $*} || ~ $#* 0){ usage exit usage } SOURCE
/src/cmd/getflags.c /src/cmd/usage.c SEE ALSO
arg(3) GETFLAGS(8)
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