Escape special character in terminal but not in script

Asked Oct 22 '17 at 03:51

Active Oct 22 '17 at 04:22

Viewed 29 times

In terminal, we should use escape character for this command

echo "Hello\!"

But in script, we don't need to use escape character for last command. Actually to produce same output, we can't use escape character. Why is there a difference between terminal and script?

asked Oct 22 '17 at 03:51

michael

Scripts don't have a history, so why should history operations be allowed? – Ignacio Vazquez-Abrams Oct 22 '17 at 03:54
@xxfelixxx you need if using quote – michael Oct 22 '17 at 03:56
You can just use single quotes and avoid the history substitution. `echo 'Hello!'` – xxfelixxx Oct 22 '17 at 03:59
@xxfelixxx Didn't notice that is a history substitution at first. So if i write this command to a .sh file, it is not treated as a history substitution? – michael Oct 22 '17 at 04:08
Yes, it will work the same. – xxfelixxx Oct 22 '17 at 04:10
@xxfelixxx but i don't need to use escape character for same command in .sh file, and it will print Hello! – michael Oct 22 '17 at 04:12
You can turn off history substitution in the shell if you want to have identical behavior in both. – xxfelixxx Oct 22 '17 at 04:13
1

`set +H` disables history substitution in the interactive shell. – xxfelixxx Oct 22 '17 at 04:15
@xxfelixxx why there are different behaviours? That is my intention to ask this question – michael Oct 22 '17 at 04:15
Because when running commands from the interactive terminal, it is handy to be able to use history substitution. A consequence of this is that now the `!` character has to be treated differently. – xxfelixxx Oct 22 '17 at 04:20
@michael, it's different because history expansion is an extension for interactive use only, and is off by default in noninteractive shells. – Charles Duffy Oct 22 '17 at 04:22
@xxfelixxx not get what you mean. What seems to me is in terminal ! is treated as history substitution, but in script ! is not treated as that, not sure why there is difference here – michael Oct 22 '17 at 04:23
@CharlesDuffy Yeah, this makes sense to me, thx – michael Oct 22 '17 at 04:24
Yes, that is correct. Interactive vs Script bash are different environments. Have a read of `man bash` for details. – xxfelixxx Oct 22 '17 at 04:24

Escape special character in terminal but not in script

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