On Thu, 2003-08-28 at 14:28, Kurt Yoder wrote: > So I'm trying to get amverify to verify "nttar" and "gtar" backups. > I've looked at this part of the amverify script from amanda 2.4.2p2: > > if [ X"$1" = X"program" -a X"$2" != X"" ]; then > if [ X"$TAR" != X"" -a X"$2" = X"$TAR" ]; then > CMD=$TAR > ARGS="tf -" > elif [ X"$TAR" != X"" \ > -a X"$SAMBA_CLIENT" != X"" \ > -a X"$2" = X"$SAMBA_CLIENT" ]; then > CMD=$TAR > ARGS="tf -" > elif [ X"$TAR" != X"" \ > -a X`basename $2` = X`basename $TAR` ]; then > CMD=$TAR > ARGS="tf -" > > But I don't understand it. If $1 is "tar", oes X"$1" = X"program" > compare "Xtar" to "Xprogram"? What are all these X's for?
Shell doesn't like empty strings, so the X guarantees that the strings will not be empty on either side of the comparison. It still comes out the same. Xtar = Xtar is that same as tar = tar, but it prevents tar = "", by turning it to Xtar = X.
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