Shell – Why $SHELL doesn’t change when I run new shell

The main differences between running a command from cron and running on the command line are:

• cron is probably using a different shell (generally /bin/sh);
• cron is definitely running in a small environment (which ones depends on the cron implementation, so check the cron(8) or crontab(5) man page; generally there's just HOME, perhaps SHELL, perhaps LOGNAME, perhaps USER, and a small PATH);
• cron treats the % character specially (it is turned into a newline);
• cron jobs run without a terminal or graphical environment.

The following invocation will run the shell snippet pretty much as if it was invoked from cron. I assume the snippet doesn't contain the characters ' or %.

env - HOME="$HOME" USER="$USER" PATH=/usr/bin:/bin /bin/sh -c 'shell snippet' </dev/null >job.log 2>&1

See also executing a sh script from the cron, which might help solve your problem.

A general rule of aliases: if it gets too complex for an alias, use a function instead.

tomcat_id () {
  ps -ef | grep catalina | grep -v grep | awk -F' ' '{print $2}'
}

The problem with your alias definition is that you got the quoting wrong. The line that defines the alias is a shell command and is parsed by the shell. Since you used double quotes, and there are probably no positional parameters at the time (so $2 expands to an empty string), the alias you've defined is

ps -ef | grep catalina | grep -v grep | awk -F' ' '{print }'

The easy way to define an alias is to use single quotes for the definition, and avoid using single quotes in the aliased command. While I'm at it, I've removed -F " ", which is the default anyway (and a bit weird because it looks like “a space” but means “any sequence of whitespace”).

alias tomcat_id='ps -ef | grep catalina | grep -v grep | awk "{print \$2}"'

Or you can use '\'' to effectively quote a single quote inside a single-quoted literal.

alias tomcat_id='ps -ef | grep catalina | grep -v grep | awk '\''{print \$2}'\'

But, as I wrote above, use a function, it's clearer. Or rather, use the appropriate tool for the job:

alias tomcat_id='pgrep catalina'

or

alias tomcat_id='pidof catalina'