diff --git a/sys/man/8/zerotrunc b/sys/man/8/zerotrunc
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+.TH ZEROTRUNC 8
+.SH NAME
+zerotrunc \- truncate input on zero byte
+.SH SYNOPSIS
+.B aux/zerotrunc
+.SH DESCRIPTION
+.PP
+.B Zerotrunc
+copies input to output until reading a first zero byte or end-of-file.
+.SH EXAMPLES
+.B Zerotrunc
+can be used to read metadata of Plan 9 image files, e. g.:
+.IP
+.EX
+% aux/zerotrunc < /dev/window
+.EE
+.SH SOURCE
+.B /sys/src/cmd/aux/zerotrunc.c
+.SH "SEE ALSO"
+.IR cat (1)