在shell脚本中编写$

Question

I have a problem while I use $ in my script

#!/bin/sh

grep -e ' H2O ' molfra.out > H2O
grep -e ' C6F13 ' molfra_ig.out > C6F13
grep -e ' C8F17 ' molfra_ig.out > C8F17
grep -e ' C10F21 ' molfra_ig.out > C10F21
grep -e ' C16F33 ' molfra_ig.out > C16F33

cat > SNW_CFscheck.gnplt << EOF
reset
set terminal png enhanced
set output '800K_Chains.png'
set title "250 water and PFPE chained SNW 800K NVT MD"
set yrange [0:4]
set ytics 1
set grid
set xlabel "Time(ps)"
set ylabel "Number of molecules"
plot "C6F13" u ($1/10000):2 w l title "800K C_6F_{13}", \
  "C8F17" u ($1/10000):2 w l title "800K C_8F_{17}", \
  "C10F21" u ($1/10000):2 w l title "800K C_{10}F_{21}", \
  "C16F33" u ($1/10000):2 w l title "800K C_{16}F_{33}"
EOF

gnuplot SNW_CFscheck.gnplt

So, I create a file named 'SNW_CFscheck.gnplt' using cat command, and execute the file But $1 is not recognized inside the cat command, (or $1 is recognized as global variable?) so the code doesn't work.

How can I use $ inside this scripts?

Thanks

Answer 1

If you want $1 not to be expanded then quote the EOF like this:

cat > SNW_CFscheck.gnplt << 'EOF'
reset
set terminal png enhanced
set output '800K_Chains.png'
set title "250 water and PFPE chained SNW 800K NVT MD"
set yrange [0:4]
set ytics 1
set grid
set xlabel "Time(ps)"
set ylabel "Number of molecules"
plot "C6F13" u ($1/10000):2 w l title "800K C_6F_{13}", \
  "C8F17" u ($1/10000):2 w l title "800K C_8F_{17}", \
  "C10F21" u ($1/10000):2 w l title "800K C_{10}F_{21}", \
  "C16F33" u ($1/10000):2 w l title "800K C_{16}F_{33}"
EOF

As per man bash :

If any characters in word are quoted, the delimiter is the result of quote removal on word, and the lines in the here-document are not expanded.

Answer 2

Did you try using an escape character? Like "\\$"?

Answer 3

Try escaping the character within double quotes "\\$". Read more about the effect of Single vs Double quotes here ---> http://linux.101hacks.com/bash-scripting/quotes-inside-shell-script/