Ubuntu – Why ‘echo $(cat /path/to/fileName)’ list the files and directions

command lineecho

When I printout the content of a file with echo $(cat /path/to/filename), it list my files and directions too. But when I do with printf "$(cat /path/to/filename)\n" it works fine.

I tried also saving it into a variable content='cat /path/to/filename' (also content=$(cat /path/to/filename) and then print by echo $content, but I getting the same result (list files and directions).

I want to store the content of the file into variable and pass the variable into my script as an input to next command.

Note that the content of my file has special character * in it.

Best Answer

Because after performing command substitution, the shell perform word splitting (or field splitting) on the result if you don't quote them.

POSIX defined word expansion as:

The order of word expansion shall be as follows:

Tilde expansion (see Tilde Expansion), parameter expansion (see Parameter Expansion), command substitution (see Command Substitution), and arithmetic expansion (see Arithmetic Expansion) shall be performed, beginning to end. See item 5 in Token Recognition.

Field splitting (see Field Splitting) shall be performed on the portions of the fields generated by step 1, unless IFS is null.

Pathname expansion (see Pathname Expansion) shall be performed, unless set -f is in effect.

Quote removal (see Quote Removal) shall always be performed last.

In your case, * matched all thing in current working directory. You must quote the result to get the expected output:

echo "$(cat /path/to/fileName)"

Related Solutions

Grep Command – How to Find Specific Words in All Files

The script below searches (text)files in a given directory recursively, for occurrences of a given string, no matter if it is in upper or lowercase, or any combination of those.

It will give you a list of found matches, the paths to the files, combined with the filenam and the actual occurrences of the string in the file, looking like:

/path/to/file1 ['numlock', 'numlocK']
/longer/path/to/file2 ['NuMlOck']

etc.

To limit the search time, I would look for matches in specific directories, so not for 2TB of files ;).

To use it:

1] Copy the text below, paste it into an empty textfile (gedit). 2] Edit the two lines in the headsection to define the string to look for and the directory to search. 3] Save it as searchfor.py. 4] To run it: open a terminal, type python3+space, then drag the script on to the terminalwindow and press return. The list of found matches will appear in the terminalwindow

In case of an error, the script will mention it.

#!/usr/bin/python3
import os
#-----------------------------------------------------
# give the searched word here in lowercase(!):
searchfor = "string_to_look_for"
# give the aimed directory here:
searchdir = "/path/to/search"
#-----------------------------------------------------
wordsize = len(searchfor)
unreadable = []
print("\nFound matches:")
for root, dirs, files in os.walk(searchdir, topdown=True):
    for name in files:
        file_subject = root+"/"+name
        try:
            with open(file_subject) as check_file:
                words = check_file.read()
                words_lower = words.lower()
                found_matches_list = [i for i in range(len(words_lower)) if words_lower.startswith(searchfor, i)]
                found_matches = [words[index:index+wordsize] for index in found_matches_list]
                if len(found_matches) != 0:
                    print(file_subject, found_matches)
                else:
                    pass
        except Exception:
            unreadable.append(file_subject)
if len(unreadable) != 0:
    print("\ncould not read the following files:")
    for item in unreadable:
        print("unreadable:", item)

Ubuntu – File list command line (hidden and subfolders)

With bash

Assuming the disk in question is mounted under /media/disk1:

$ shopt -s globstar dotglob
$ stat -c '"%n",%s,%y' /media/disk1/**/* >disk1.csv

shopt -s globstar dotglob turns on recursive globbing feature of bash (enables use of '**', see https://unix.stackexchange.com/questions/49913/recursive-glob). It also turns on matching of files starting with a ., als known as hidden files.

stat is the program used to get file meta data. Basically this program will be run for each file on the disk.

-c '"%n",%s,%y' specifies the output format for the stat command. %n is the file name, enclosed in double quotes, %s is the file size, %y is the last modification time. (see stat --help)

/media/disk1/**/* tells bash to hand all the file names recursively found under that path to the pogram (stat), for both, normal and hidden files, since dotglob is enabled.

>disk1.csv redirects output into a file named disk1.csv.

The output in disk1.csv will look like this for my home for instance:

$ stat -c '"%n",%s,%y' /home/seb/**/*
"/home/seb/111",82,2018-03-26 18:38:04.048099912 +0200
"/home/seb/app",4096,2017-07-13 23:39:06.509862769 +0200
"/home/seb/Applications",4096,2018-03-14 20:20:48.552005660 +0100
"/home/seb/Applications/arduino-1.8.2",4096,2017-05-29 20:45:01.184017517 +0200
"/home/seb/Applications/arduino-1.8.2/arduino",946,2017-03-22 13:32:41.000000000 +0100
[...]

I tested to import the resulting csv into libreoffice calc and it worked nicely, also with funny file names with line breaks in them. It will probably choke on file names with double quotes in them.

ARG_MAX

The above command will fail if the total number of files is too high or the total number of characters in all file names is too high. For small drives (USB thumb drives etc.) it should be enough, but if you are indexing a big disk with millions of files you would probably hit that limit.

You can run the following instead, it will produce the same output (and eat less memory):

find /media/disk1 -type f -print0 | xargs -0 stat -c '"%n",%s,%y' >disk1.csv

For the "find .. -print0 | xargs -0 .." pattern you will find many answers here already, e. g. Difference between "xargs" and command substitution?