Why can't I find the command bash: Is: cannot find the command

Why can't we find the command bash: Is: the command-Linux general technology-Linux technology and application information Is not found. The following Is a detailed description. Example
To install the software today, first download a tz package and check how to install it online. The result Is half installed. When the make command Is used, the file does not exist and then the Is command Is used, the result is as follows:



Jun @ jun-laptop :~ $ Is
Bash: Is: Command not found
Jun @ jun-laptop :~ $ Cd/media
Jun @ jun-laptop:/media $ Is
Bash: Is: Command not found
Jun @ jun-laptop:/media $./Is
Bash:./Is: the file or directory does not exist.
Jun @ jun-laptop:/media $ is
Bash: is: Command not found
Jun @ jun-laptop:/media $./is
Bash:./is: the file or directory does not exist.
Jun @ jun-laptop:/media $ help
GNU bash, version 3.2.39 (1)-release (i486-pc-linux-gnu)
Shell commands are defined internally. Enter "help" to view the list.
Enter "help name" to find more information about the "name" command function.
Enter "info bash" to view more information about shell.
Enter "man-k" or "info" to view the command information that is not listed in this list.
Commands with asterisks (*) are forbidden.

JOB_SPEC [&] (expression ))
. Filename [arguments]:
[Arg...] [[expression]
Alias [-p] [name [= value]...] bg [job_spec...]
Bind [-lpvsPVS] [-m keymap] [-f fi break [n]
Builtin [shell-builtin [arg...] caller [EXPR]
Case WORD in [PATTERN [| PATTERN]. cd [-L |-P] [dir]
Command [-pVv] command [arg...] compgen [-abcdefgjksuv] [-o option
Complete [-abcdefgjksuv] [-pr] [-o continue [n]
Declare [-afFirtx] [-p] [name [= val dirs [-clpv] [+ N] [-N]
Disown [-h] [-ar] [jobspec...] echo [-neE] [arg...]
Enable [-pnds] [-a] [-f filename] eval [arg...]
Exec [-cl] [-a name] file [redirec exit [n]
Export [-nf] [name [= value]...] or false
Fc [-e ename] [-nlr] [first] [last fg [job_spec]
For NAME [in WORDS...;] do COMMA for (exp1; exp2; exp3); do COM
Function NAME {COMMANDS;} or NA getopts optstring name [arg]
Hash [-lr] [-p pathname] [-dt] [na help [-s] [pattern...]
History [-c] [-d offset] [n] or hi if COMMANDS; then COMMANDS; [elif
Jobs [-lnprs] [jobspec...] or job kill [-s sigspec |-n signum |-si
Let arg [arg...] local name [= value]...
Logout popd [+ N |-N] [-n]
Printf [-v var] format [arguments] pushd [dir | + N |-N] [-n]
Pwd [-LP] read [-ers] [-u fd] [-t timeout] [
Readonly [-af] [name [= value]...] return [n]
Select NAME [in WORDS...;] do CO set [-- abefhkmnptuvxBCHP] [-o opti
Shift [n] shopt [-pqsu] [-o long-option] opt
Source filename [arguments] suspend [-f]
Test [expr] time [-p] PIPELINE
Times trap [-lp] [arg signal_spec...]
True type [-afptP] name [name...]
Typeset [-afFirtx] [-p] name [= valu ulimit [-SHacdfilmnpqstuvx] [limit
Umask [-p] [-S] [mode] unalias [-a] name [name...]
Unset [-f] [-v] [name...] until COMMANDS; do COMMANDS; done
Variables-Some variable names an wait [n]
While COMMANDS; do COMMANDS; done {COMMANDS ;}
Jun @ jun-laptop:/media $

Is command Is my first use