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For example after doing apt-get update, it shows Reading package lists... 82% with the percentage changing in the same line.

How is that achieved? Is it possible to use it in a bash script?

Gilles 'SO- stop being evil'
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user80551
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2 Answers2

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Terminals understand escape sequences to move the cursor around, change the text color and other actions. These escape sequences are recorded in the termcap and terminfo databases as they differ between terminal types (altough most terminal types today mostly implement the same escape sequences).

You can record the full output of an application with the script utility.

script -c 'apt-get update' apt-get.script

apt-get keeps things simple: it only uses the control character carriage return (known as CR, Ctrl+M, \r, …) which moves the cursor to the beginning of the current line.

Gilles 'SO- stop being evil'
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if you haven't output new line yet (e,g: used -n in echo command) , the command:

echo -e "\r\033["

will do the trick.

Ohad Cohen
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  • What is `\033[` part meant to do? It seems `\r` should be enough to do carriage return. – Ruslan May 28 '16 at 18:31
  • it should remove the text shown (`\r` get you back to the start of the line, but if you don't write anything the text won't be removed) now I checked this on few other terminals, and the `\033[` behaves differently in any terminal, so I would recommend not to use it in scripts. – Ohad Cohen May 29 '16 at 09:06
  • To clear the terminal instead of just doing carriage return I'd suggest something like `printf \\r%${COLUMNS}s\\r ' '`. – Ruslan May 29 '16 at 09:54