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Shell: count the number of files in a folder..complicated

Cloturernapasdesensfigure Posted messages 117 Status Membre -
UnGnU Posted messages 1468 Status Contributeur - 22 Jun 2016 at 16:06

Hello,

I would like to place an order, or a series of orders, or create a script to count the number of files in a directory, and if the "ls" fails, display an error. I want to emphasize that I want to execute ls and display an error if it fails, not to determine in advance whether ls will fail.

For testing, I created:
A folder named aa containing a single file named "h h"
A folder named bb containing no files

I use ls $folder | wc -l to know the number of files.

Problem: if "ls" fails, the wc -l run in parallel still returns 0.

GNU-bash-4.1.2 $ ls
aa bb
GNU-bash-4.1.2 $ ls aa |wc -l
1
GNU-bash-4.1.2 $ ls bb |wc -l
0
GNU-bash-4.1.2 $ ls cc | wc -l
ls: cannot access cc: No such file or directory
0
GNU-bash-4.1.2 $

I tried to store the result of "ls" in a variable, but in that case I lose the last line break of the result of "ls", and wc -l gives an incorrect result.

Do you have a better idea? How would you solve this problem?
Thank you :)

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5 réponses

Réponse 1 / 5

zipe31 Posted messages 34620 Registration date Status Contributeur Last intervention 6 499

Hello,

Maybe not the most optimized solution:

ls cc >/dev/null && ls cc | wc -l

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Cloturernapasdesensfigure Posted messages 117 Status Membre 5

:)
I thought about it for a moment but didn't test it since it involves running ls twice and I didn't like that
But I have to acknowledge its effectiveness


GNU-bash-4.1.2 $ ls aa>/dev/null && ls aa | wc -l || echo ERROR
1
GNU-bash-4.1.2 $ ls bb>/dev/null && ls bb | wc -l || echo ERROR
0
GNU-bash-4.1.2 $ ls cc>/dev/null && ls cc | wc -l || echo ERROR
ls: cannot access cc: No such file or directory
ERROR
GNU-bash-4.1.2 $

I’ll take it!
Thank you!

(I will try to adapt it also with a find command to actually count the number of files including any files with a "\n" in the name. If there's no simpler dedicated command for that)

Cloturernapasdesensfigure Posted messages 117 Status Membre 5

Hello again,
I would still like to find a proper solution.

I'm struggling.
I've tried many ways, unsuccessfully, here is my last (awful) attempt:
if list="$(find aa -type f -print0)"; then od -c <<<"$list" | fgrep -o '\0' | wc -l; else echo "ERROR"; fi

I really thought I was trying to do something simple, right? Count the number of files in a directory properly.
Do you see another way to do it, please?

My difficulties:
- passing through a temporary variable loses the information of the last line break and all NULL binary characters.
(I would like to avoid creating temporary files just for that)
- placing commands between "|" in a command within $( ) makes it so that I can't tell if there was an error during the execution of the first command, even with $PIPESTATUS.

karirovax Posted messages 3584 Status Membre 215

Hello,

find /path/ -type f is for files, use -type d for directories.

karirovax Posted messages 3584 Status Membre 215

Example for the current directory if you want to know how many directories:

find . -type d -name "*" | wc -l

Réponse 3 / 5

dubcek Posted messages 18814 Registration date Status Contributeur Last intervention 5 655

hello

$ ls
aa bb
$ ls aa bb 2>/dev/null| (a=$(wc -l); [[ $a -eq 0 ]] && echo error || echo $a )
2
$ ls bb 2>/dev/null| (a=$(wc -l); [[ $a -eq 0 ]] && echo error || echo $a )
1
$ ls cc 2>/dev/null| (a=$(wc -l); [[ $a -eq 0 ]] && echo error || echo $a )
error

dubcek Posted messages 18814 Registration date Status Contributeur Last intervention 5 655

The purists will retort that I am not testing the error of ls but the absence of a file.

Cloturernapasdesensfigure Posted messages 117 Status Membre 5

Hi, indeed, it's not working right now :/ It returns an error if there are 0 files instead of returning the number of files (0).

That's right UnGnu: I want to display the number of files in a folder, whether it's 0 or n. But if the command we use to check the contents of the folder fails (for whatever reason), then we display ERROR and not 0. A file name can contain any character except the NULL character or "/", hence the idea of using find -print0, but in this case I can't count the NULL characters if I put the result in a variable.

Réponse 4 / 5

UnGnU Posted messages 1468 Status Contributeur 158

There is the command "tree" (provided it is installed) that does this very well.

$ ls
aa bb cc dd

$ ls -R
.:
aa bb cc dd

./aa:
file1 file2 file3

./bb:

./cc:
hh?hh

./dd:
file script.sed

$ tree
.
├── aa
│   ├── file1
│   ├── file2
│   └── file3
├── bb
├── cc
│   └── hh\012hh
└── dd
 ├── file
 └── script.sed

4 directories, 6 files

$ tree --prune
.
├── aa
│   ├── file1
│   ├── file2
│   └── file3
├── cc
│   └── hh\012hh
└── dd
 ├── file
 └── script.sed

3 directories, 6 files

$ tree | tail -1 | grep -Po ', \K[^ ]*'
6

$ tree aa | tail -1 | grep -Po ', \K[^ ]*'
3

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Cloturernapasdesensfigure Posted messages 117 Status Membre 5

Thank you, unfortunately I cannot install tree on this server, and I would like as much as possible a solution that is not dependent on certain packages to do something that seems so simple at first glance, as it would quickly lead to other problems.
Otherwise, tree does count the files but in case of an error it always displays 0 files and returns 0 as the return code!

zipe31 Posted messages 34620 Registration date Status Contributeur Last intervention 6 499 > Cloturernapasdesensfigure Posted messages 117 Status Membre

but in case of error

What error?

Cloturernapasdesensfigure Posted messages 117 Status Membre 5

Error when unable to access the folder, for example if it is empty:

GNU-bash-4.1.2 $ tree nonexistent_folder
nonexistent_folder [error opening dir]

0 directories, 0 files
GNU-bash-4.1.2 $ echo $?
0

zipe31 Posted messages 34620 Registration date Status Contributeur Last intervention 6 499 > Cloturernapasdesensfigure Posted messages 117 Status Membre

Bad example, here the folder is not empty, it does not exist, which contradicts your reasoning, namely, and I quote you:
display the number of files in a folder, whether it's 0 or n
which suggests that the folders exist.

Cloturernapasdesensfigure Posted messages 117 Status Membre 5

Hello,
no, I had written: I want to display the number of files in a folder, whether it is 0 or n. But if the command we use to know the contents of the folder fails (for any reason), then we display ERROR and not 0.
I will try to be precise: I want to make a script that takes a folder name as a parameter (with the full path) and tries to read this folder to find out how many files it contains (excluding the contents of subfolders)
if there are n files in the folder: display n
if there is 1 file in the folder: display 1
if the folder is empty: display 0
So we expect an existing and accessible folder. But if we cannot determine the contents of the folder, either because it does not exist, we do not have the rights, a network mount is faulty, a disk is failing, unable to execute a command of the script correctly (execution rights on a command, memory saturation, ...), if we fail we display ERROR.

To illustrate: I was doing a script to display the number of files in a folder using “ls folder |wc -l” And I thought it would be good to check the return of ls and display ERROR if ls fails, otherwise wc will display 0 in case of a problem, for example if the folder is deleted and no longer exists, and that wouldn't be acceptable at all.

...While writing, I just thought of this solution:

var=$(ls bb) && if [ ${#var} -ne 0 ]; then wc -l <<< "$var"; else echo "0"; fi || echo ERREUR

which works every time (it separately handles the case of an empty folder).

I don't know what you think of this solution; if you have a better idea, I am open to it.
Notably, it no longer works if a file contains a newline in its name (ls displays one file per line and wc will count it as 2 files).

Réponse 5 / 5

dubcek Posted messages 18814 Registration date Status Contributeur Last intervention 5 655

$ ls
aa bb
$ a=$(ls 2>/dev/null ); [[ $? -ne 0 ]] && a=error || a=$(wc -l <<<"$a") ; echo $a
2
$ a=$(ls aa 2>/dev/null ); [[ $? -ne 0 ]] && a=error || a=$(wc -l <<<"$a") ; echo $a
1
$ a=$(ls cc 2>/dev/null ); [[ $? -ne 0 ]] && a=error || a=$(wc -l <<<"$a") ; echo $a
error

Cloturernapasdesensfigure Posted messages 117 Status Membre 5

In the case of an empty file, $a is interpreted as a line, and wc -l returns 1 instead of 0.
I had also tried this approach, the problem is that when we store the output of a command in $a, we lose the information about whether or not there was a final newline. :\
(this will not work either if a filename contains a newline, it will be considered as 2 files)

Shell: count the number of files in a folder..complicated

5 réponses

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