5.6.3. How to run sed ?¶

There are two ways of running sed:

you can give the commands on the command line:
```
sed 's/yes/done/' file
```
If you want to use several commands, you have to use the -e option:
```
sed -e 's/yes/done/' -e 's/no/not-done/' file
```
it is also possible to place the commands in a seperate file:
```
sed -f sedsrc file
```
where sedsrc contains the necessary commands.

Exercises

On our parallel machines, the nodes where the command can run are listed in the file /usr/spool/machines. However the first node is mentioned 2 times. How can we remove the first line of this file, so that each node is mentioned one time ? How can we count how many nodes we have in this parallel environment ? (Use the command wc)

An example file is at /data/tccm/linux_bash/5/machines
How can we use machines from previous exercises to duplicate each node, so to make a machines file where each node is mentioned two times ?
How should you make a general gaussian-inputfile, where the number of processors is not specified but filled in on run-time ?
- to get the number of cores available, see in the file /proc/cpuinfo and use grep and wc 1
- to specify the number of procs in a gaussian-inputfile, you have to add a line like:
```
%nprocshared=8
```
How can you make this general so that the number is always correct for the node where the job is running ?

You can store the output of a command in a variable by including the command in $(…), (see this section) For example

biggest_file=$(ls -lSr | tail -1)