Make script executable from within script itself

Question

I would like a script that will show me the percentage of reserved blocks. If it can done another way, that is good.

This works if I manually make it executable. Can I make it executable from within the script itself?

cat > somescript.sh << \EOF
#!/bin/bash

block_count=$(sudo tune2fs -l /dev/sda1 | awk '/^Block count:/ {print $NF}')
reserved_block_count=$(sudo tune2fs -l /dev/sda1 | awk '/^Reserved block count:/ {print $NF}')

perl -e 'printf("%.1lf%%\n", ($ARGV[0] * 100.0 ) / $ARGV[1])' "$reserved_block_count" "$block_count"
EOF

Answer 1

Answer to your question

Of course that’s possible – but I’d not consider it good style. See below for a better solution.

If you run a shell and give it the script file as an argument it will execute it regardless of the absence of a shebang or any execution bit:

$ cat no_script
chmod +x /path/to/no_script
$ ls -l no_script
-rw-rw-r-- 1 dessert dessert 24 Jun 12 22:59 script
$ bash no_script
$ ls -l no_script
-rwxrwxr-x 1 dessert dessert 24 Jun 12 22:59 script

If the script is executed multiple times you probably don’t want to call chmod without any need every time, so just test for the file being not executable:

[ ! -x /path/to/script ] && chmod +x /path/to/script

As for your script, awk can do the whole thing in a single call:

#!/bin/bash
tune2fs -l /dev/sda1 | awk '/^Block count:/{a=$NF}/^Reserved block count:/{b=$NF}END{printf "%.1f%%\n", b/a*100}'

I removed the sudo because you don’t use it in a script – run the whole script as root instead.

Solution to your problem

I read from your question that you’re bothered by the two steps necessary to set up a script. Let’s write a script that helps with that:

#!/bin/bash
cat <&0 >"$1" &&
chmod +x "$1"

cat <&0 >"$1" makes cat read from stdin and write to the script file you give it as the first argument. Save this as e.g. makescript and make it executable with chmod +x /path/to/makescript. Now if you want to write a script, simply do it like that:

/path/to/makescript /path/to/new/script <<EOF … EOF

If you don’t want to type /path/to/makescript every time, define an alias like makescript=/path/to/makescript in your ~/.bash_aliases or ~/.bashrc or move it to a directory in your PATH.

Example run

$ echo -e '#!/bin/bash\ncat <&0 >"$1" &&\nchmod +x "$1"' >makescript
$ chmod +x makescript 
$ ./makescript a_test_script <<EOF
> #!/bin/bash
> echo a script
> EOF
$ ls -l *script
-rwxrwxr-x 1 dessert dessert 26 Jun 13 12:44 a_test_script
-rwxrwxr-x 1 dessert dessert 43 Jun 13 12:44 makescript
$ ./a_test_script 
a script

The sky is the limit.

Answer 2

If you want to write the script's content and make it executable in the same command (sorta), you can simply add the chmod after the cat:

$ cat > somescript.sh << \EOF && chmod a+x somescript.sh && sudo ./somescript.sh
#!/bin/bash
# Show percentage of reserved blocks
#
tune2fs -l /dev/sda5 |
     awk '/^Block count:/{bc=$NF}
          /^Reserved block count:/{rbc=$NF}
          END{printf "%.1f%%\n", (rbc*100)/bc}'
EOF

I also took the liberty of simplifying your script a bit. You're already using awk, so you may as well do the whole thing there.

Answer 3

cat > somescript.sh << \EOF
#!/bin/bash
# Show percentage of reserved blocks

block_count=$(sudo tune2fs -l /dev/sda1 | awk '/^Block count:/ {print $NF}')
reserved_block_count=$(sudo tune2fs -l /dev/sda1 | awk '/^Reserved block count:/ {print $NF}')

perl -e 'printf("%.1lf%%\n", ($ARGV[0] * 100.0 ) / $ARGV[1])' "$reserved_block_count" "$block_count"
EOF

chmod +x somescript.sh

somescript.sh