$ set -vx

$ echo `/bin/echo \`pwd\` `
echo `/bin/echo \`pwd\` `
/bin/echo `pwd`
pwd
+++ pwd
++ /bin/echo /home/users/tongsun/txtHist
+ echo /home/users/tongsun/txtHist
/home/users/tongsun/txtHist

$ echo `/bin/echo  \`basename \\\`pwd\\\`\` `
echo `/bin/echo  \`basename \\\`pwd\\\`\` `
/bin/echo  `basename \`pwd\``
basename `pwd`
pwd
++++ pwd
+++ basename /home/users/tongsun/txtHist
++ /bin/echo txtHist
+ echo txtHist
txtHist

$ echo $(/bin/echo  $(basename $(pwd)))
echo $(/bin/echo  $(basename $(pwd)))
/bin/echo  $(basename $(pwd))
basename $(pwd)
pwd
++++ pwd
+++ basename /home/users/tongsun/txtHist
++ /bin/echo txtHist
+ echo txtHist
txtHist