Bash – echo string >> file does not work

Don’t believe everything a computer tells you.

$ ps -p $$
PID TTY          TIME CMD
3744 pts/1    00:00:03 bash
$ ps -t pts/1
PID TTY          TIME CMD
3744 pts/1    00:00:03 bash
4285 pts/1    00:00:00 ps
$ echo foo | while read x
do
        ps -t pts/1
done
PID TTY          TIME CMD
3744 pts/1    00:00:03 bash
4287 pts/1    00:00:00 bash
4288 pts/1    00:00:00 ps

$ echo "$$, $BASHPID"
3744, 3744
$ echo foo | while read x
do
        echo "$$, $BASHPID"
        ps -t pts/1
done
3744, 4292
PID TTY          TIME CMD
3744 pts/1    00:00:03 bash
4292 pts/1    00:00:00 bash
4293 pts/1    00:00:00 ps

When you do some_command | while …, the shell puts the while loop into a subshell, but $$ continues to report the PID of the main (parent) process.  In bash, $BASHPID reveals the truth.

Consider doing

while read alias
do
  alias "$alias"
done << EOF
s=screen
v=vlock -a
j=jobs
EOF

Note: I've assumed you're teaching yourself Bash. Do not use this code in production. find "$directory" -maxdepth 1 -type d will get you the directories, -type f will get you the files.

Since it is complaining about line 16, let's have a look at it:

$dirs=`ls $1`

If you want to assign to a variable, you should not include the $. I'm guessing you meant:

dirs=`ls $1`

What's happening now, is this:

• $dirs is probably empty, so substituted with nothing.
• The ls command is run, and its output substituted in the 'command'.
• The first file in your directory is called Calibre, leaving you with the command: =Calibre x y z ...
• =Calibre is not a valid command, thus the error.

However, we're not there yet: this will go wrong if there are spaces in any of the filenames. To fix that, you need to do more:

• You need to include IFS=$'\n' somewhere before the for loop. This sets the fields separator to the linefeed character, which stops the for loop from splitting up the files on the spaces or tabs (it's technically possible for a file to have a linefeed in its filename as well: you're unlikely to ever encounter such a file and it won't cause serious problems in this case if you do run into such a file, but it's worth being aware of the possibility in case it ever does matter).
• In order for a filename with spaces not to turn into several different arguments to -f and -d, you need to put quotes $i. (So: [ -f "$i" ] and [ -d "$i" ]. In order to support directories with spaces in them, you should do the same for $1 where it is used.