Read All Files in a Directory Into an Array Unix

📅 April viii, 2017
Bash arrays can be tricky, so hither are a few hints to assistance agreement.

Quick Notes:

• Create an Array: declare -a arrPics
• Become Assortment Length: echo "${#arrPics[@]}"
• Get All Elements equally Dissever Items: echo "${arrPics[@]}"
• Get All Elements equally a Single Line: echo "${arrPics[*]}"
• Delete an Array: unset arrPics
• Remove a Specific Element: unset arrPics[0]
• List All Indices: echo "${!arrPics[@]}"
• Get Length of Specific Chemical element: echo "${@arrPics[0]}"

Create the Assortment

Suppose we accept a directory of images, and we want to add the filename of each to the same Bash assortment.

#!/bin/fustigate  declare -a arrPics for file in *.jpg practise     arrPics=("${Pics[@]}" "$file") done

          declare -a arrPics        

Declares an array. Empty by default, and indexed starting at 0. A Fustigate array is dynamic: It tin grow and compress every bit elements are added and removed, and then yous do not need to specify a fixed array size like other languages crave.

Nosotros could likewise declare the array as

arrPics=()

and this would accomplish the same consequence. declare with the -a selection makes information technology clear that we are declaring an assortment. (The parentheses () might get confused with $() during a cursory glance.) Both work.

          for file in *.jpg; practise ... washed        

This gets the filenames of all files in the current directory that finish with .jpg. In this case, this is what we want. Retrieve that Bash is case-sensitive, so files catastrophe in .JPG  will be ignored.

          arrPics=(${arrPics[@]} "$file")        

This is the statement that performs the work of adding each new filename to the array. We are adding the array itself each time in lodge to preserve the existing array contents. If we did…

arrPics=("$file")

…then the array would only consist of 1 element — the terminal filename found.

How Many Elements in the Assortment?

echo ${#arrPics[@]}

will return the number of items in the array. Notation the # character.

Show the Array

echo "${arrPics[@]}"

This will list the contents of the array on one line.

Sample Output:

P1240738.jpg P1240739.jpg P1240741.jpg P1240742.jpg P1240744.jpg P1240747.jpg P1240749.jpg P1240750.jpg P1240751.jpg P1240752.jpg P1240753.jpg P1240754.jpg P1240755.jpg P1240756.jpg P1240757.jpg P1240758.jpg

Some other Listing:

echo "${arrPics[*]}"

This will besides evidence the assortment elements in a single line.

P1240738.jpg P1240739.jpg P1240741.jpg P1240742.jpg P1240744.jpg P1240747.jpg P1240749.jpg P1240750.jpg P1240751.jpg P1240752.jpg P1240753.jpg P1240754.jpg P1240755.jpg P1240756.jpg P1240757.jpg P1240758.jpg

What is the Different Between [@] and [*] ?

This a tricky point to recall because the output in a higher place looks the same. All the same, the deviation is significant.

[@] means: Output the elements as Individual items.

[*] ways: Output the elements as ONE item.

Depending upon the Internal Field Separator (echo $IFS), which is normally set to a space or whitespace by default, assortment elements will be separated by the IFS character. You can change IFS to anything you want: IFS="." would separate past the dot character. The default is fine.

Hither is a short script for demonstration:

#!/bin/bash  declare -a arrPics  for file in *.jpg practice     arrPics=(${arrPics[*]} "$file") washed  # Using [@] echo -e '\nUsing [@] -----------------------------------' for particular in "${arrPics[@]}" do     echo "Particular: *** $item ***" washed  # Using [*] repeat -east '\nUsing [*] -----------------------------------' for particular in "${arrPics[*]}" do     echo "ITEM: *** $particular ***" done

We put a listing of .jpg filenames into an array the same as before, but nosotros bear witness the contents using a for loop. Each loop iteration should put each chemical element on its own line in the output. We use two loops: I with [@] and the second using [*].

Using [@] ----------------------------------- Particular: *** P1240738.jpg *** Item: *** P1240739.jpg *** Detail: *** P1240741.jpg *** Particular: *** P1240742.jpg *** ITEM: *** P1240744.jpg *** ITEM: *** P1240747.jpg *** Particular: *** P1240749.jpg *** ITEM: *** P1240750.jpg *** ITEM: *** P1240751.jpg *** Item: *** P1240752.jpg *** ITEM: *** P1240753.jpg *** Particular: *** P1240754.jpg *** ITEM: *** P1240755.jpg *** ITEM: *** P1240756.jpg *** Item: *** P1240757.jpg *** ITEM: *** P1240758.jpg ***  Using [*] ----------------------------------- ITEM: *** P1240738.jpg P1240739.jpg P1240741.jpg P1240742.jpg P1240744.jpg P1240747.jpg P1240749.jpg P1240750.jpg P1240751.jpg P1240752.jpg P1240753.jpg P1240754.jpg P1240755.jpg P1240756.jpg P1240757.jpg P1240758.jpg ***

Notice the difference?

When nosotros use "${arrPics[@]}", each element in the array is treated equally a SEPARATE detail.

When we use "${arrPics[*]}", all array elements are treated as a SINGLE particular.

What can cause confusion between [@] and [*] is that their outputs will announced identical without this contrived example.

echo "${arrPics[@]}"  P1240738.jpg P1240739.jpg P1240741.jpg P1240742.jpg P1240744.jpg P1240747.jpg P1240749.jpg P1240750.jpg P1240751.jpg P1240752.jpg P1240753.jpg P1240754.jpg P1240755.jpg P1240756.jpg P1240757.jpg P1240758.jpg  echo "${arrPics[*]}"  P1240738.jpg P1240739.jpg P1240741.jpg P1240742.jpg P1240744.jpg P1240747.jpg P1240749.jpg P1240750.jpg P1240751.jpg P1240752.jpg P1240753.jpg P1240754.jpg P1240755.jpg P1240756.jpg P1240757.jpg P1240758.jpg

The for loop test reveals the divergence. Most likely, "${arrPics[@]}" is what we want. Note that double quotes are necessary to produce the issue differences.

Deleting the Array

unset arrPics

That's it. The array volition be cleared and deleted. If yous try to list its contents again, only blank lines volition appear in the terminal.

Get Range of Elements

echo "${arrPics[@]:0:iii}"

This gets the first three elements starting at index 0.

echo "${arrPics[@]:10:2}"

This gets 2 sequent elements starting at index 10. If either the starting index or the limit is out of range or nonexistent, Bash will endeavour to return what it can and ignore the residual.

Remove a Specific Chemical element

unset arrPics[0]

Removes the element at index 0. The assortment "shifts back" to fill the vacancy, so removing an element will not go out a blank value or produce a hole in the array. For instance, if arrPics[0] contains "red" and arrPics[1] contains "blueish," then arrPics[0] will contain "blue" afterwards we run unset arrPics[0].

List All Indices

repeat "${!arrPics[@]}"

This volition list all indices of the array starting at 0. If we take an array of 16 elements, and so the output will exist:

0 1 two 3 4 5 vi 7 eight 9 10 11 12 13 14 15

Get Length of Specific Chemical element

echo "${#arrPics[0]}"

This returns the length of the detail at index 0. If the string ABCDEFG.jpg exists at index 0, then the output is xi.

Annotation that we use a specific index instead of [@] or [*] like we did earlier to get the number of items in the assortment.

Conclusion

Much more is possible with Bash arrays, and so explore and take fun!

This entry was posted on April eight, 2017, 8:09 PM and is filed under linux. Yous tin can follow any responses to this entry through RSS 2.0. Y'all tin leave a response, or trackback from your ain site.

gardnerquer1990.blogspot.com

Source: https://delightlylinux.wordpress.com/2017/04/08/put-filenames-in-bash-array/

Share this post