In my continuing struggle with my menu for record manipulation, I've been scripting to add records to the 'records' file. For the most part, I've been successful. I am, however, running into a strange problem.
Code:
while [ ! $gn_correct ]
do
echo -n "Given name: "
read g_name
if [ ! $g_name ] ; then
echo "Given name not entered."
elif [ `expr substr $g_name 1 1` = " " ] ; then
echo "Given name may not begin with a space."
elif [[ $g_name = $(echo "$g_name" | tr -dc '[A-za-z ]') ]] ; then
gn_correct=1
echo -n "$g_name:" >> records
else echo "Given name can contain only alphabetic characters and spaces"
fi
# Close given name loop.
done
The above code reads in a person's given name. It makes sure that a name has been entered, then proceeds. The problem lies here:
Code:
elif [ `expr substr $g_name 1 1` = " " ] ; then
echo "Given name may not begin with a space."
The idea is to test to make sure the first character in the string received for the given name is not a space and return an error-echo if it is. It'll then repeat the loop, so the user is given another opportunity to get it right. In theory this continues until a valid given name is received.
However, it doesn't work this way. Instead, this code is skipped over. Spaces are truncated from entries with a leading space anyway - but the problem is, I'm using this same code to collect job title information. Job titles often have spaces in them (though not at the start.)
The expr continues to fail at picking up leading spaces - but, more strangely, if there is a space somewhere else in the string, expr encounters a syntax error, and the echo displays that a job title may not begin with a space.
Any suggestions on how I could detect leading spaces and produce an error, while still allowing spaces elsewhere in the string?
In my continuing struggle with my menu for record manipulation, I've been scripting to add records to the 'records' file. For the most part, I've been successful. I am, however, running into a strange problem.
Code:
while [ ! $gn_correct ]
do
echo -n "Given name: "
read g_name
if [ ! $g_name ] ; then
echo "Given name not entered."
elif [ `expr substr $g_name 1 1` = " " ] ; then
echo "Given name may not begin with a space."
elif [[ $g_name = $(echo "$g_name" | tr -dc '[A-za-z ]') ]] ; then
gn_correct=1
echo -n "$g_name:" >> records
else echo "Given name can contain only alphabetic characters and spaces"
fi
# Close given name loop.
done
The above code reads in a person's given name. It makes sure that a name has been entered, then proceeds. The problem lies here:
Code:
elif [ `expr substr $g_name 1 1` = " " ] ; then
echo "Given name may not begin with a space."
The idea is to test to make sure the first character in the string received for the given name is not a space and return an error-echo if it is. It'll then repeat the loop, so the user is given another opportunity to get it right. In theory this continues until a valid given name is received.
However, it doesn't work this way. Instead, this code is skipped over. Spaces are truncated from entries with a leading space anyway - but the problem is, I'm using this same code to collect job title information. Job titles often have spaces in them (though not at the start.)
The expr continues to fail at picking up leading spaces - but, more strangely, if there is a space somewhere else in the string, expr encounters a syntax error, and the echo displays that a job title may not begin with a space.
Any suggestions on how I could detect leading spaces and produce an error, while still allowing spaces elsewhere in the string?
Hi Dennis, I see where you're going with your suggestion, and I tried it out.
It's still not reporting the error for the leading space. There are less errors now if I feed it a string with spaces in other places, but it's still complaining that the elif has been fed too many arguments.
$ cat s
#! /bin/bash
printf 'enter name: '
while IFS= :; do
read
case $REPLY in
\ *) printf 'invalid, retry: ';;
*) printf 'ok\n';break;;
esac
done
$ ./s
enter name: initial space
invalid, retry: no_space
ok
Last edited by radoulov; 09-03-2008 at 07:42 AM..
Reason: depending on your shell, you may need to modify the IFS temporarily
Silentwolf, you're on the right track -- but the if statement won't work without double-quoting the space on the left-side. And then it won't work because the expansion of g_name results in a space gobbled up by the parser before finding its way to expr. Just prefix the expression with a character and get the 2nd character.
Code:
elif [ "`expr substr X$g_name 2 1`" = " " ] ; then
echo "Given name may not begin with a space."
But I think there is a simpler way:
Code:
elif [ "`echo $g_name`" = "$g_name" ] ; then
echo "Given name may not begin with a space."
HOWEVER, that will fail if the name contains MULTIPLE spaces or trails with a space (the echo command will seemingly "compress" each into one space and cut off the ending spaces).
Finally, if using ksh or bash, you can use the ${#%} operators, such as this:
Code:
elif [ " ${g_name# }" = "$g_name" ] ; then
echo "Given name may not begin with a space."
This strips the leading space of g_name if it's there, then prefixes the space to g_name. If that is different than $g_name, it means the strip failed. There are other ways to do this, like:
Code:
elif [ "${g_name# }" != "$gname" ] ; then
echo "Given name may not begin with a space."
OR
Code:
elif [ "${g_name%% *}" = "" ] ; then
echo "Given name may not begin with a space."
Which is the reverse -- you cut everything after the space, including the space, and if the resulting string is empty, the cut succeeded and started with the first character of the string, ie, the first character was blank.
The problem is that most shells will strip leading and trailing IFS characters, so you need to modify the IFS value(s) temporarily (see my post above).
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Ensuring A String Doesn't Begin With Space