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I am currently taking a Controlled Assessment in a Computing GCSE and this is the task.
At the command prompt, type ls -a. Demonstrate and explain what happens. Modify this command so that it only shows hidden files beginning with the letter ‘b’.
I have already done ls -a and I tried ls -b, but it didn't work.
The names of hidden files start with . (dot), there are none that start with b. To list names starting with .b use
$ ls .b*
This will also list the contents of any directory whose name starts with .b. Note that -a is not needed here as we explicitly give a filename pattern for the shell to match. Since the pattern starts with . (dot), it will match hidden files. The expanded pattern will be given to ls for processing.
To avoid listing the contents of directories, use
$ ls -d .b*
The above solutions will give an error if no name matches the pattern.
To only list the names of regular files whose names start with .b, use
$ for name in .b*; do test -f "$name" && printf '%s\n' "$name"; done
To get the output in a similar way as with plain ls (note that column is a non-standard utility):
$ for name in .b*; do test -f "$name" && printf '%s\n' "$name"; done | column
The last couple of solutions will not print anything of no name matches the pattern.
regular, a find command would be much simpler: find -maxdepth 1 -type f -name '.b*'. Also faster than a for loop. However, I assume ls-usage was intended.
– Fiximan
Feb 23 '17 at 10:02
find is able to do it that way, of course. Standard find needs a search path, and doesn't understand -maxdepth. This will also generate output with ./ prepended to the name (with GNU find).
– Kusalananda♦
Feb 23 '17 at 10:06
ls is the command, and -a is the flag for the command.
In order to see the files staring from b one can specify a pattern - .b*
Where . means that the files are hidden and the * means everything else...
and in general when you don't know what a command does, read the manual - man ls
For avoiding listing of the contents of the listed items, use the -d option.
ls -a | grep .b*should do I think – ddnomad Feb 23 '17 at 9:24greping anlsoutput is unnecessarily complex, when you can specify the pattern withls -a -d .b*- note that you need-dfor not listing contents of the results. Also thatgrepwill show files like123.bWRONG. – Fiximan Feb 23 '17 at 9:35man ls. I suggest you read it. – terdon♦ Feb 23 '17 at 9:54