CODEWITHSUNDEEP
perlshellksh
Russell
Russell

Reputation: 4085

Shell script date arithmetics

Here's my high level problem.

I want to read a number max_age_in_secs from a config file. This number represents the number of seconds we consider a file is "old". After we read this config, we want to search all files in a directory data and delete all files modified before max_age_in_secs seconds ago.

This has to be done as a shell script, more specifically korn shell.

What I'm doing right now is to touch a dummy file to be modified max_age_in_secs ago, then use find and its ! -newer option to search for files older than that.

I'm having a problem getting a timestamp to pass to touch. The date command on my unix box doesn't have the option --date so I can't use that.

I'm looking at perl -e "blah_blah_blah" but I need to pass the max_age_in_secs variable to the perl command. The only way I know to do that is creating a new .pl file and pass arguments to that file. But ideally I would like to have this functionality in one korn script file. A workaround may be constructing a perl_command variable, and execute its content, but I think that's not secure and vulnerable to injections.

But I'm relatively new to shell scripting and perl, so any help is appreciated.

Upvotes: 0

Views: 403

Answers (3)

mob
mob

Reputation: 118595

There is more than one way to pass an environment variable from a shell to a one-line perl command:

  • Directly. Most shells (including korn) interpolate expressions inside double quotes.
perl -e "print $VAR"

so in this case $VAR is coming from the shell. This technique has a lot of shortcomings, namely that with an `-e "double quoted expression" it is a pain to use other Perl variables or use a lot of other useful Perl constructions that might be misconstrued by the shell.

  • As a command line argument, accessed in the perl script in @ARGV
perl -e 'print "VAR is $ARGV[0]"' $VAR

This will do if you don't need to use @ARGV (which are implicitly used if you use the -p or -n switches, or if your program uses the default <> operator).

  • Through Perl's %ENV hash.
perl -e 'print "VAR is $ENV{VAR}"'

This mechanism doesn't interfere with @ARGV

Upvotes: 2

dogbane
dogbane

Reputation: 274532

Instead of seconds use minutes. Recent versions of find have the mmin option. For example, the following commands delete files older than a minute.

find /path/ -type f -mmin +1 -exec rm {} \;

Upvotes: 0

user3458
user3458

Reputation: 

perl -e '... $ENV{max_age_in_secs}...'

as long as you do 

export max_age_in_secs

in bash/sh/ksh

Upvotes: 1

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