Let's say the variable numbers=$@ where $@is from user input. The user typed in ./script.sh 901.32.02 and I want to get the first digit 9 and store in another variable. How can I do this? I was told to do
for n in `seq 1 $count` do var=${numbers[0]} done but that prints out the whole input if I echo $var instead of just 9.
In Bash, you can extract the first character using parameter expansion:
${parameter:offset:length} Example:
$ var=901.32.02 $ first_char="${var:0:1}" $ echo "${first_char}" 9 
"${numbers%%.*}") which gives a different output (901). numbers='901.32.02' firstdigit="${numbers:0:1}" printf 'The first digit is "%s"\n' "$firstdigit" The result of the above is
The first digit is "9" The ${numbers:0:1} parameter expansion in bash give you the substring of length 1 from the start of the string (offset zero). This is a bash-specific parameter substitution (also in some other shells, but not in the POSIX standard).
In a POSIX shell, you may also do
firstdigit=$( printf "%s\n" "$numbers" | cut -c 1 ) This will use cut to only return the first character.
Or, using standard parameter expansions,
firstdigit="${numbers%${numbers#?}}" This first uses ${numbers#?} to create a string with the first digit removed, then it removes that string from the end of $numbers using ${numbers%suffix} (where suffix is the result of the first expansion).
The above assumes that the first character of $numbers is actually a digit. If it is not, then you would have to first remove non-digits from the start of the value:
numbers=$( printf '%s\n' "$numbers" | sed 's/^[^0-9]*//' ) or,
numbers="${numbers#${numbers%%[0-9]*}}" ${numbers[0]} would have worked if each character was a separate element in the array numbers (and if the first character was a digit). Since numbers is not an array, it's equivalent to just $numbers.
printf "%.1s" 1234 should do, without needing the cut You can use below method too
cat script.sh #!/bin/bash echo $1 | awk '{print substr($1,1,1)}' sh script.sh 90 Where 90 is the user input output is 9
awk from your bash script and store the results in a bash script variable! #!-line must not be preceded by blank lines or spaces. You are also specifying bash as the script language in the script itself, while running it with sh. With colrm
echo '901.32.02' | colrm 2 If you want to detect only digits (not other character types) you should use a simple regular expression.
[[ ${numbers} =~ ^([[:digit:]]) ]] && var=${BASH_REMATCH[1]} In $var is a digit or it is empty (even not declared).
