Run two commands with a crontab

cdcrondebianshell

I have a quick question. I need to add a cron to my debain crontab using an automated shell script and I need the cron to do two things:

cd into /etc/application
run the command "scrapy crawl"

crontab -l | { /bin/cat; /bin/echo "* 3 * * * cd /etc/application"; }
| crontab –

How do I get it to also run the scrapy crawl command?

Best Answer

You can have multiple commands in a single crontab line. Just separate them with semicolons:

crontab -l | { /bin/cat; /bin/echo "* 3 * * * cd /etc/application ; scrapy crawl"; } | crontab -

Related Solutions

Ruby – How to call shell commands from Ruby

This explanation is based on a commented Ruby script from a friend of mine. If you want to improve the script, feel free to update it at the link.

First, note that when Ruby calls out to a shell, it typically calls /bin/sh, not Bash. Some Bash syntax is not supported by /bin/sh on all systems.

Here are ways to execute a shell script:

cmd = "echo 'hi'" # Sample string that can be used

Kernel#` , commonly called backticks – `cmd`

This is like many other languages, including Bash, PHP, and Perl.

Returns the result (i.e. standard output) of the shell command.

Docs: http://ruby-doc.org/core/Kernel.html#method-i-60
```
value = `echo 'hi'`
value = `#{cmd}`
```
Built-in syntax, %x( cmd )

Following the x character is a delimiter, which can be any character. If the delimiter is one of the characters (, [, {, or <, the literal consists of the characters up to the matching closing delimiter, taking account of nested delimiter pairs. For all other delimiters, the literal comprises the characters up to the next occurrence of the delimiter character. String interpolation #{ ... } is allowed.

Returns the result (i.e. standard output) of the shell command, just like the backticks.

Docs: https://docs.ruby-lang.org/en/master/syntax/literals_rdoc.html#label-Percent+Strings
```
value = %x( echo 'hi' )
value = %x[ #{cmd} ]
```
Kernel#system

Executes the given command in a subshell.

Returns true if the command was found and run successfully, false otherwise.

Docs: http://ruby-doc.org/core/Kernel.html#method-i-system
```
wasGood = system( "echo 'hi'" )
wasGood = system( cmd )
```
Kernel#exec

Replaces the current process by running the given external command.

Returns none, the current process is replaced and never continues.

Docs: http://ruby-doc.org/core/Kernel.html#method-i-exec
```
exec( "echo 'hi'" )
exec( cmd ) # Note: this will never be reached because of the line above
```

Here's some extra advice: $?, which is the same as $CHILD_STATUS, accesses the status of the last system executed command if you use the backticks, system() or %x{}. You can then access the exitstatus and pid properties:

$?.exitstatus

For more reading see:

How to use SSH to run a local shell script on a remote machine

If Machine A is a Windows box, you can use Plink (part of PuTTY) with the -m parameter, and it will execute the local script on the remote server.

plink root@MachineB -m local_script.sh

If Machine A is a Unix-based system, you can use:

ssh root@MachineB 'bash -s' < local_script.sh

You shouldn't have to copy the script to the remote server to run it.

Best Answer

Related Solutions

Ruby – How to call shell commands from Ruby

How to use SSH to run a local shell script on a remote machine

Related Topic