Files Processing

Files processing

The for loop works well when we need to process a list of files. The only point here is to compose the loop condition correctly. There are several common mistakes when writing this condition. Let’s consider them by examples.

The first example is a script that reads the current directory and prints the types of all files there. We can call the file utility to get this information for each file.

When composing the for loop condition, the most common mistake is to neglect patterns (known as “globbing”). Users often call the ls or find utility to get the STRING, like this:

for filename in $(ls)
for filename in $(find . -type f)

However, both of these for conditions are wrong. They lead to the following problems:

1. Word splitting breaks the names of files and directories with spaces.
2. If the filename contains an asterisk, Bash performs globbing before it starts the loop. Then, it writes the globbing result to the filename variable. This way, we lose the actual filename.
3. The output of the ls utility depends on the regional settings. Therefore, we can get question marks instead of the national alphabet characters in filenames. In that case, the for loop cannot process the files.

We must always use patterns in the for condition when we need to enumerate filenames. It is the only correct solution for this task.

We should write the following for loop condition for our script:

for filename in *

The for-file.sh shows the complete script.