I have a script which measures how long some command executes.

It needs the "real" `time` command, meaning, a binary for example in `/usr/bin/time` (as the bash-built-in doesn't have the `-f`flag).

Below, a simplified script which can be debugged:

```
#!/bin/bash

TIMESEC=$(echo blah | ( /usr/bin/time -f %e grep blah >/dev/null ) 2>&1 | awk -F. '{print $1}')

echo ABC--$TIMESEC--DEF

if [ "$TIMESEC" -eq 0 ] ; then
   echo "we are here!"
fi

```

Save as "test.sh" and execute:

```
$ bash test.sh
ABC--0--DEF
we are here!

```

So it worked.

Now, let's try to debug this by adding "-x" to bash command line:

```
$ bash -x test.sh
++ echo blah
++ awk -F. '{print $1}'
+ TIMESEC='++ /usr/bin/time -f %e grep blah
0'
+ echo ABC--++ /usr/bin/time -f %e grep blah 0--DEF
ABC--++ /usr/bin/time -f %e grep blah 0--DEF
+ '[' '++ /usr/bin/time -f %e grep blah
0' -eq 0 ']'
test.sh: line 10: [: ++ /usr/bin/time -f %e grep blah
0: integer expression expected

```

Why does this script break when we're using "-x", and works fine without it?