Quick Tips

A running list of quick tips for the terminal/shell scripting.

Removing Character From File

This tip is useful when uploading files to the Linux terminal on JSLinux. For some reason when I uploaded a certain text file it added ^M on each blank line and some seemingly random locations. So I used cat and tr to remove each instance of the characters. This can be done with:

cat -v filename | tr -d 'char' > output.file

The -v shows non-printing/control characters. The -d after the tr command delete the specified character. The > will take the output of the command(s) and write it to a file.

Replacing Characters in a File

So when I was working on the title randomizer project I wanted to show the code on the webpage. To show HTML tags, for example (<html>) you have to use the special HTML codes for them to show on the webpage. There are many ways replace text in a file such as python, perl, shell script, and terminal commands. In the Linux terminal one easy way is to use sed:

sed 's/</\</g; s/>/\>/g' title.js > title.txt

Here the s is for substitute and the g is for global so the characters are replaced for every instance, not just the first one found in the file. Because the & is used by the terminal/shell you have to escape the character with a blackslash \. You can do multiple replacements separated with a semicolon ;.

This can also be done in Windows with Powershell.

(((Get-Content title.js -Raw) -replace '<','<') -replace '>','>') | Set-Content title.txt

Powershell allows you to "nest" commands with the parenthesis. So we get the raw javascript file and replace the < and the > with HTML codes, then pipe that output to Set-Content and write it to title.txt.