Shell Programming and Scripting

./construct_operon.sh: line 5: [: -gt: unary operator expected

#!/bin/bash
# Construct Operons using gene pairs.
rm -rf operons_result
lines=`awk 'END {print NR}' ecoli_operons`
while [ $lines -gt 0 ];
do
    head -1 ecoli_operons | awk '{print $1"\n"$2}' > pattern
    grep -f pattern ecoli_operons | awk '{print $1"\n"$2}' > temp
    pat_count=`grep -f pattern -v temp | awk 'END {print NR}'`
    while [ $pat_count -gt 0 ];
    do
        cat temp >> pattern
        grep -f pattern ecoli_operons | awk '{print $1"\n"$2}' > temp
        pat_count=`grep -f pattern -v temp | awk 'END {print NR}'`
    done
    grep -f pattern ecoli_operons | awk '{print $1"\n"$2}' | sort -u | awk '{printf $0"\t"} END {printf"\n"}' >> operons_result
    grep -f pattern -v ecoli_operons > temp1
    mv temp1 ecoli_operons
    echo $lines
    lines=`awk 'END {print NR}' ecoli_operons`
done
rm -rf temp
rm -rf pattern

while [[ $lines -gt 0 ]]
do
commands
done

[[ ]]
test.
Test expression between [[ ]]. This is a shell keyword

The [[ ]] construct is the more versatile Bash version of [ ]. This is the extended test command, adopted from
ksh88.
No filename expansion or word splitting takes place between [[ and ]], but there is parameter expansion
and command substitution.
file=/etc/passwd
if [[ -e $file ]]
then
echo "Password file exists."
fi
Using the [[ ... ]] test construct, rather than [ ... ] can prevent many logic errors in scripts. For example,
the &&, ||, <, and > operators work within a [[ ]] test, despite giving an error within a [ ] construct.