BASH convert a text file line by line into variables - linux

Question

I want to make a script for an automated setup for a multiseat system. First action is
lspci | grep -i 'vga\|graphic' | cut -b 1-7 > text.txt
Now i want to put the two lines of the file into variables. My dowdy solution was this:
VAR1=$(head -n 1 text.txt)
VAR2=$(tail -n 1 text.txt)
It also works, however, there's probably a better solution to convert a text file line by line into variables.

Answer 1

The following should achieve exactly what you're doing, without the use of a temporary file
#!/bin/bash
{ read -r var1 _ && read -r var2 _; } < <(lspci | grep -i 'vga\|graphics')
Now, if you have several lines from lspci | grep -i 'vga\|graphics' (or just one, or none), you might want something more general, i.e., put the results in an array:
#!/bin/bash
var=()
while read -r f _; do var+=( "$f" ); done < <(lspci | grep -i 'vga\|graphics')
# display the content of var
declare -p var
If you have a recent version of Bash, and you love mapfile and awk (but who doesn't?), you could also do something like this:
#!/bin/bash
mapfile -t var < <(lspci | awk 'tolower($0) ~ /var|graphics/ { print $1 }')
# display the content of var
declare -p var
For a Pure Bash possibility (except for lspci, of course):
#!/bin/bash
shopt -s extglob
var=()
while read -r v rest; do
[[ ${rest,,} = *#(vga|graphics)* ]] && var+=( "$v" )
done < <(lspci)
# display var
declare -p var
This uses:
Lower case conversion of rest with ${rest,,}
Pattern matching and extended globs with *#(vga|graphics)* (to avoid regular expressions altogether).

Answer 2

If you can format your text file into name value pairs, you could use bash associative arrays to store and reference each item. Note in this code = is used as the delimiter to separate the name value pair.
#read in fast config (name value pair file)
declare -A MYMAP
while read item; do
NAME=$(cut -d "=" -f1 <<<"$item")
VALUE=$(cut -d "=" -f2 <<<"$item")
MYMAP["$NAME"]="$VALUE"
done <./config_file.txt
#size of map
MYMAP_N=${#MYMAP[#]}
#make a list of keys
KEYS=("${!MYMAP[#]}")
#dereference map
SELECTION="${MYMAP["my_first_key"]}"

Answer 3

If the values do not contain spaces, in bash using the array variable:
declare -a vars
eval "vars=(`echo line1; echo line2`)" # the `echo ...` simulates your command
echo number of values: ${#vars[#]}
for ((I = 0; I < ${#vars[#]}; ++I )); do
echo value \#$I is ${vars[$I]}
done
echo all values : ${vars[*]}
The trick is to generate the statement initializing the array with the values, and then eval it.
If the values have spaces/special characters, then escaping/quoting might be necessary.

Answer 4

read VAR1 VAR2 < <(sed -n '1p;$p' myfile | tr '\n' ' ')
This ought to do what you need it uses process substitution to print the lines you want and then redirects them to the variables, if you want different lines just build this statement as you need with a for loop putting whatever lines you want if you want them all use wc to count the lines, then build VAR1 .. VAR[n] and sed -n '1p;2p;3p..[n]p' and you then can eval the built statement.