How do I create a new empty file in a bash script?

Question

I have to remove a lot of font-family: declarations from my website, they are hundreds and I have replaced most of them with the same line, only commented (ex: /* font-family: "Segoe UI","Helvetica","Arial"; */).

Now, if I could only search for the un-commented ones to find the few that are left. My first atempt clearly demonstrates I do not fully understand regular expressions:

^(?!(?:/*)).*\s*."font-family:"."*"

The syntax is Boost (but only a subpart of it, as the replacement is PCRE-style).

Solution 1

Use touch command. touch filename.txt.

Solution 2

Use the null command (:) redirect (> filename) trick (:>), as this will truncate to zero or create the named file.

$ echo foo > filea
$ :> filea
$ wc -c filea
       0 filea
$ rm filea
$ :> filea
$ wc -c filea
       0 filea

(This will fail if the shell sets a NOCLOBBER option.)

Solution 3

The shortest way:

>filename

Solution 4

You could always use perl, too.

$ stat filename.txt
stat: cannot stat 'filename.txt': No such file or directory
$ perl -e 'open($fh,">","filename.txt") or die $!;close($fh)'                                         
$ stat filename.txt                                                                                   
  File: 'filename.txt'
  Size: 0           Blocks: 0          IO Block: 4096   regular empty file
Device: 801h/2049d  Inode: 280728      Links: 1
Access: (0664/-rw-rw-r--)  Uid: ( 1000/ xieerqi)   Gid: ( 1000/ xieerqi)
Access: 2017-02-08 13:51:01.479121995 -0700
Modify: 2017-02-08 13:51:01.479121995 -0700
Change: 2017-02-08 13:51:01.479121995 -0700
 Birth: -

Solution 5

dd can be used to create an empty file as follows:

dd if=/dev/null of=filename.txt count=0

One case where dd is more useful than the other approaches is creating an EFI variable (PK) through the efivars filesystem (/sys/firmware/efi/efivars).

One some platforms and Linux distributions, the file is created with the "immutible" attribute set (shows up as the "i" flag with "lasattr"). So, any subsequent operations on the file fail.

For example, touch not only creates the file, but sets the time stamp on the file. Similarly, piping to the file with > not only creates the file, but performs additional operations that fail. The dd command does not appear to fail the same way.

View more solutions

Comments

[Wiktor Stribiżew]

If you are using Find and Replace, the regex syntax is Boost (but only a subpart of it, as the replacement is PCRE-style).

[Ioan-Radu Tanasescu]

Ok, thanks :) editing question.

[Wiktor Stribiżew]

So, you just want to keep /*...*/ comments and remove font-family: "..","..."; everywhere else?

[Ioan-Radu Tanasescu]

I want to not find the commented ones, and wrap the rest in comment tags, but a replace all is not needed, simply finding them is enough, there are not too many left. This somewhat works: ^(?!(?:/*)).*\s*.font-family:.*

[Wiktor Stribiżew]

Could you please check my approach? I "ignore" font-family inside the comments, and remove all others, but I am not sure what the final output is required.

[Ioan-Radu Tanasescu]

I have tried, thank you, it also finds other comments :)

[Ioan-Radu Tanasescu]

As I said, it returns other results as well, including stuff wrapped in comments :)

[Wiktor Stribiżew]

Then please clarify with examples. In Boost syntax, you cannot use (*SKIP)(*F) verbs, you must match and capture. I find the question rather unclear now.

[Ioan-Radu Tanasescu]

Ok, so I want to run a search that will find all font-family: strings not preceded by a comment tag. So the search should return ALL lines containing font-family:+WHATVER but NOT return /* font-family:+WHATVER

[Wiktor Stribiżew]

Like ^(?:(?!/\*).)*\s*font-family:.*? I fixed your tempered greedy token.

[Ioan-Radu Tanasescu]

Works awesome, all my upvotes are belong to you :) post it so I can chose it as correct answer.

[Wiktor Stribiżew]

Sorry, wife is grumbling too much, I will add explanations later.

[Hannu]

echo -n >file

[ilkkachu]

Just > filename.txt would do, no need for the :. Or >> filename.txt if we don't want to trash it if it does happen to exist.

[can-ned_food]

@ilkkachu although the question does specify Bash, using : does make the script more likely to accomplish its task with other shells e.g. Zsh.

[johanvdw]

take care - this will not empty your file if it already exists

[andrewz]

Actually I tried touch and "echo -n > file" inside my bash script but I get an error when I execute the script: "No such file or directory" on that line. Can someone help please?

[DevonDahon]

Best answer. Couldn't be shorter.