How to test for certain characters in a file - linux

Question

I am currently running a script with an if statement. Before I run the script, I want to make sure the file provided as the first argument has certain characters.
If the file does not have those certain characters in certain spots then the output would be else "File is Invalid" on the command line.
For the if statement to be true, the file needs to have at least one hyphen in Field 1 line 1 and at least one comma in Field one Line one.
How would I create an if statement with perhaps a test command to validate those certain characters are present?
Thanks
Im new to Linux/Unix, this is my homework so I haven't really tried anything, only brain storming possible solutions.
function usage
{
echo "usage: $0 filename ..."
echo "ERROR: $1"
}
if [ $# -eq 0 ]
then
usage "Please enter a filename"
else
name="Yaroslav Yasinskiy"
echo $name
date
while [ $# -gt 0 ]
do
if [ -f $1 ]
then
if <--------- here is where the answer would be
starting_data=$1
echo
echo $1
cut -f3 -d, $1 > first
cut -f2 -d, $1 > last
cut -f1 -d, $1 > id
sed 's/$/:/' last > last1
sed '/last:/ d' last1 > last2
sed 's/^ *//' last2 > last3
sed '/first/ d' first > first1
sed 's/^ *//' first1 > first2
sed '/id/ d' id > id1
sed 's/-//g' id1 > id2
paste -d\ first2 last3 id2 > final
cat final
echo ''
else
echo
usage "Coult not find file $1"
fi
shift
done
fi

Answer 1

In answer to your direct question:
For the if statement to be true, the file needs to have at least one
hyphen in Field 1 line 1 and at least one comma in Field one Line one.
How would I create an if statement with perhaps a test command to
validate those certain characters are present?
Bash provides all the tools you need. While you can call awk, you really just need to read the first line of the file into two-variable (say a and b) and then use the [[ $a =~ regex ]] to where the regex is an extended regular expression that verifies that the first field (contained in $a) contains both a '-' and ','.
For details on the [[ =~ ]] expression, see bash(1) - Linux manual page under the section labeled [[ expression ]].
Let's start with read. When you provide two variables, read will read the first field (based on normal word-splitting given by IFS (the Internal Field Separator, default $'[ \t\n]' - space, tab, newline)). So by doing read -r a b you read the first field into a and the rest of the line into b (you don't care about b for your test)
Your regex can be ([-]+.*[,]+|[,]+.*[-]+) which is an (x|y), e.g. x OR y expression where x is [-]+.*[,]+ (one or more '-' and one or more ','), your y is [,]+.*[-]+ (one or more ',' and one or more '-'). So by using the '|' your regex will accept either a comma then zero-or-more characters and a hyphen or a hyphen and zero-or-more characters and then a comma in the first field.
How do you read the line? With simple redirection, e.g.
read -r a b < "$1"
So your conditional test in your script would look something like:
if [ -f $1 ]
then
read -r a b < "$1"
if [[ $a =~ ([-]+.*[,]+|[,]+.*[-]+) ]] # <-- here is where the ...
then
starting_data=$1
...
else
echo "File is Invalid" >&2 # redirection to 2 (stderr)
fi
else
echo
usage "Coult not find file $1"
fi
shift
...
Example Test Files
$ cat valid
dog-food, cat-food, rabbit-food
50lb 16lb 5lb
$ cat invalid
dogfood, catfood, rabbitfood
50lb 16lb 5lb
Example Use/Output
$ read -r a b < valid
if [[ $a =~ ([-]+.*[,]+|[,]+.*[-]+) ]]; then
echo "file valid"
else
echo "file invalid"
fi
file valid
and for the file without the certain characters:
$ read -r a b < invalid
if [[ $a =~ ([-]+.*[,]+|[,]+.*[-]+) ]]; then
echo "file valid"
else
echo "file invalid"
fi
file invalid
Now you really have to concentrate on eliminating the spawning of at least a dozen subshells where you call cut 3-times, sed 7-times, paste once and then cat. While it is good you are thinking through what you need to do, and getting it working, as mentioned in my comment, any time you are looping, you want to eliminate the number of subshells spawned to the greatest extent possible. I suspect as #Mig answered, awk will be the proper tool that can likely eliminate all 12 subshells are replace it with a single call to awk.

Answer 2

I personally would use awk for this all part since you want to test fields and create a string with concatenated fields. Awk is perfect for that.
But here is a small script which shows how you could just test your file's first line:
if [[ $(head -n 1 file.csv | awk '$1~/-/ && $1~/,/ {print "MATCH"}') == 'MATCH' ]]; then
echo "yes"
else
echo "no"
fi
It looks overkill when not doing the whole thing in awk but it works. I am sure there is a way to test only one regex, but that would involve knowing which flavour of awk you have because I think they don't all use the same regex engine. Therefore I left this out for the sake of simplicity.